16 files changed, 3639 insertions, 0 deletions

diff --git a/test/unit/data/cacheable-object.js b/test/unit/data/cacheable-object.js
new file mode 100644
index 0000000..8c31a5b
--- /dev/null
+++ b/test/unit/data/cacheable-object.js
@@ -0,0 +1,355 @@
+import t from 'tap';
+
+import CacheableObject from '#cacheable-object';
+
+function newCacheableObject(PD) {
+  return new (class extends CacheableObject {
+    static propertyDescriptors = PD;
+  });
+}
+
+t.test(`CacheableObject simple separate update & expose`, t => {
+  const obj = newCacheableObject({
+    number: {
+      flags: {
+        update: true
+      }
+    },
+
+    timesTwo: {
+      flags: {
+        expose: true
+      },
+
+      expose: {
+        dependencies: ['number'],
+        compute: ({ number }) => number * 2
+      }
+    }
+  });
+
+  t.plan(1);
+  obj.number = 5;
+  t.equal(obj.timesTwo, 10);
+});
+
+t.test(`CacheableObject basic cache behavior`, t => {
+  let computeCount = 0;
+
+  const obj = newCacheableObject({
+    string: {
+      flags: {
+        update: true
+      }
+    },
+
+    karkat: {
+      flags: {
+        expose: true
+      },
+
+      expose: {
+        dependencies: ['string'],
+        compute: ({ string }) => {
+          computeCount++;
+          return string.toUpperCase();
+        }
+      }
+    }
+  });
+
+  t.plan(8);
+
+  t.equal(computeCount, 0);
+
+  obj.string = 'hello world';
+  t.equal(computeCount, 0);
+
+  obj.karkat;
+  t.equal(computeCount, 1);
+
+  obj.karkat;
+  t.equal(computeCount, 1);
+
+  obj.string = 'testing once again';
+  t.equal(computeCount, 1);
+
+  obj.karkat;
+  t.equal(computeCount, 2);
+
+  obj.string = 'testing once again';
+  t.equal(computeCount, 2);
+
+  obj.karkat;
+  t.equal(computeCount, 2);
+});
+
+t.test(`CacheableObject combined update & expose (no transform)`, t => {
+  const obj = newCacheableObject({
+    directory: {
+      flags: {
+        update: true,
+        expose: true
+      }
+    }
+  });
+
+  t.plan(2);
+
+  obj.directory = 'the-world-revolving';
+  t.equal(obj.directory, 'the-world-revolving');
+
+  obj.directory = 'chaos-king';
+  t.equal(obj.directory, 'chaos-king');
+});
+
+t.test(`CacheableObject combined update & expose (basic transform)`, t => {
+  const obj = newCacheableObject({
+    getsRepeated: {
+      flags: {
+        update: true,
+        expose: true
+      },
+
+      expose: {
+        transform: value => value.repeat(2)
+      }
+    }
+  });
+
+  t.plan(1);
+
+  obj.getsRepeated = 'dog';
+  t.equal(obj.getsRepeated, 'dogdog');
+});
+
+t.test(`CacheableObject combined update & expose (transform with dependency)`, t => {
+  const obj = newCacheableObject({
+    customRepeat: {
+      flags: {
+        update: true,
+        expose: true
+      },
+
+      expose: {
+        dependencies: ['times'],
+        transform: (value, { times }) => value.repeat(times)
+      }
+    },
+
+    times: {
+      flags: {
+        update: true
+      }
+    }
+  });
+
+  t.plan(3);
+
+  obj.customRepeat = 'dog';
+  obj.times = 1;
+  t.equal(obj.customRepeat, 'dog');
+
+  obj.times = 5;
+  t.equal(obj.customRepeat, 'dogdogdogdogdog');
+
+  obj.customRepeat = 'cat';
+  t.equal(obj.customRepeat, 'catcatcatcatcat');
+});
+
+t.test(`CacheableObject validate on update`, t => {
+  const mockError = new TypeError(`Expected a string, not ${typeof value}`);
+
+  const obj = newCacheableObject({
+    directory: {
+      flags: {
+        update: true,
+        expose: true
+      },
+
+      update: {
+        validate: value => {
+          if (typeof value !== 'string') {
+            throw mockError;
+          }
+          return true;
+        }
+      }
+    },
+
+    date: {
+      flags: {
+        update: true,
+        expose: true
+      },
+
+      update: {
+        validate: value => (value instanceof Date)
+      }
+    }
+  });
+
+  let thrownError;
+  t.plan(6);
+
+  obj.directory = 'megalovania';
+  t.equal(obj.directory, 'megalovania');
+
+  t.throws(
+    () => { obj.directory = 25; },
+    {cause: mockError});
+
+  t.equal(obj.directory, 'megalovania');
+
+  const date = new Date(`25 December 2009`);
+
+  obj.date = date;
+  t.equal(obj.date, date);
+
+  t.throws(
+    () => { obj.date = `TWELFTH PERIGEE'S EVE`; },
+    {cause: TypeError});
+
+  t.equal(obj.date, date);
+});
+
+t.test(`CacheableObject transform on null value`, t => {
+  let computed = false;
+
+  const obj = newCacheableObject({
+    spookyFactor: {
+      flags: {
+        update: true,
+        expose: true,
+      },
+
+      expose: {
+        transform: value => {
+          computed = true;
+          return (value ? 2 * value : -1);
+        },
+      },
+    },
+  });
+
+  t.plan(4);
+
+  t.equal(obj.spookyFactor, -1);
+  t.ok(computed);
+
+  computed = false;
+  obj.spookyFactor = 1;
+
+  t.equal(obj.spookyFactor, 2);
+  t.ok(computed);
+});
+
+t.test(`CacheableObject don't transform on successful update`, t => {
+  let computed = false;
+
+  const obj = newCacheableObject({
+    original: {
+      flags: {
+        update: true,
+        expose: true,
+      },
+
+      update: {
+        validate: value => value.startsWith('track:'),
+      },
+
+      expose: {
+        transform: value => {
+          computed = true;
+          return (value ? value.split(':')[1] : null);
+        },
+      },
+    },
+  });
+
+  t.plan(4);
+
+  t.doesNotThrow(() => obj.original = 'track:foo');
+  t.notOk(computed);
+
+  t.equal(obj.original, 'foo');
+  t.ok(computed);
+});
+
+t.test(`CacheableObject don't transform on failed update`, t => {
+  let computed = false;
+
+  const obj = newCacheableObject({
+    original: {
+      flags: {
+        update: true,
+        expose: true,
+      },
+
+      update: {
+        validate: value => value.startsWith('track:'),
+      },
+
+      expose: {
+        transform: value => {
+          computed = true;
+          return (value ? value.split(':')[1] : null);
+        },
+      },
+    },
+  });
+
+  t.plan(4);
+
+  t.throws(() => obj.original = 'album:foo');
+  t.notOk(computed);
+
+  t.equal(obj.original, null);
+  t.ok(computed);
+});
+
+t.test(`CacheableObject default update property value`, t => {
+  const obj = newCacheableObject({
+    fruit: {
+      flags: {
+        update: true,
+        expose: true
+      },
+
+      update: {
+        default: 'potassium'
+      }
+    }
+  });
+
+  t.plan(1);
+  t.equal(obj.fruit, 'potassium');
+});
+
+t.test(`CacheableObject default property throws if invalid`, t => {
+  const mockError = new TypeError(`Expected a string, not ${typeof value}`);
+
+  t.plan(1);
+
+  let thrownError;
+
+  t.throws(
+    () => newCacheableObject({
+      string: {
+        flags: {
+          update: true
+        },
+
+        update: {
+          default: 123,
+          validate: value => {
+            if (typeof value !== 'string') {
+              throw mockError;
+            }
+            return true;
+          }
+        }
+      }
+    }),
+    {cause: mockError});
+});
diff --git a/test/unit/data/composite/control-flow/exposeConstant.js b/test/unit/data/composite/control-flow/exposeConstant.js
new file mode 100644
index 0000000..0c75894
--- /dev/null
+++ b/test/unit/data/composite/control-flow/exposeConstant.js
@@ -0,0 +1,42 @@
+import t from 'tap';
+
+import {compositeFrom, continuationSymbol, input} from '#composite';
+import {exposeConstant} from '#composite/control-flow';
+
+t.test(`exposeConstant: basic behavior`, t => {
+  t.plan(2);
+
+  const composite1 = compositeFrom({
+    compose: false,
+
+    steps: [
+      exposeConstant({
+        value: input.value('foo'),
+      }),
+    ],
+  });
+
+  t.match(composite1, {
+    expose: {
+      dependencies: [],
+    },
+  });
+
+  t.equal(composite1.expose.compute(), 'foo');
+});
+
+t.test(`exposeConstant: validate inputs`, t => {
+  t.plan(2);
+
+  t.throws(
+    () => exposeConstant({}),
+    {message: `Errors in input options passed to exposeConstant`, errors: [
+      {message: `Required these inputs: value`},
+    ]});
+
+  t.throws(
+    () => exposeConstant({value: 'some dependency'}),
+    {message: `Errors in input options passed to exposeConstant`, errors: [
+      {message: `value: Expected input.value() call, got dependency name`},
+    ]});
+});
diff --git a/test/unit/data/composite/control-flow/exposeDependency.js b/test/unit/data/composite/control-flow/exposeDependency.js
new file mode 100644
index 0000000..8f6bfd0
--- /dev/null
+++ b/test/unit/data/composite/control-flow/exposeDependency.js
@@ -0,0 +1,64 @@
+import t from 'tap';
+
+import {compositeFrom, continuationSymbol, input} from '#composite';
+import {exposeDependency} from '#composite/control-flow';
+
+t.test(`exposeDependency: basic behavior`, t => {
+  t.plan(4);
+
+  const composite1 = compositeFrom({
+    compose: false,
+
+    steps: [
+      exposeDependency({dependency: 'foo'}),
+    ],
+  });
+
+  t.match(composite1, {
+    expose: {
+      dependencies: ['foo'],
+    },
+  });
+
+  t.equal(composite1.expose.compute({foo: 'bar'}), 'bar');
+
+  const composite2 = compositeFrom({
+    compose: false,
+
+    steps: [
+      {
+        dependencies: ['foo'],
+        compute: (continuation, {foo}) =>
+          continuation({'#bar': foo.toUpperCase()}),
+      },
+
+      exposeDependency({dependency: '#bar'}),
+    ],
+  });
+
+  t.match(composite2, {
+    expose: {
+      dependencies: ['foo'],
+    },
+  });
+
+  t.equal(composite2.expose.compute({foo: 'bar'}), 'BAR');
+});
+
+t.test(`exposeDependency: validate inputs`, t => {
+  t.plan(2);
+
+  t.throws(
+    () => exposeDependency({}),
+    {message: `Errors in input options passed to exposeDependency`, errors: [
+      {message: `Required these inputs: dependency`},
+    ]});
+
+  t.throws(
+    () => exposeDependency({
+      dependency: input.value('some static value'),
+    }),
+    {message: `Errors in input options passed to exposeDependency`, errors: [
+      {message: `dependency: Expected dependency name, got input.value() call`},
+    ]});
+});
diff --git a/test/unit/data/composite/control-flow/withResultOfAvailabilityCheck.js b/test/unit/data/composite/control-flow/withResultOfAvailabilityCheck.js
new file mode 100644
index 0000000..2bcabb4
--- /dev/null
+++ b/test/unit/data/composite/control-flow/withResultOfAvailabilityCheck.js
@@ -0,0 +1,195 @@
+import t from 'tap';
+
+import {compositeFrom, continuationSymbol, input} from '#composite';
+import {withResultOfAvailabilityCheck} from '#composite/control-flow';
+
+const composite = compositeFrom({
+  compose: false,
+
+  steps: [
+    withResultOfAvailabilityCheck({
+      from: 'from',
+      mode: 'mode',
+    }).outputs({
+      ['#availability']: '#result',
+    }),
+
+    {
+      dependencies: ['#result'],
+      compute: ({'#result': result}) => result,
+    },
+  ],
+});
+
+t.test(`withResultOfAvailabilityCheck: basic behavior`, t => {
+  t.plan(1);
+
+  t.match(composite, {
+    expose: {
+      dependencies: ['from', 'mode'],
+    },
+  });
+});
+
+const quickCompare = (t, expect, {from, mode}) =>
+  t.equal(composite.expose.compute({from, mode}), expect);
+
+const quickThrows = (t, {from, mode}) =>
+  t.throws(() => composite.expose.compute({from, mode}));
+
+t.test(`withResultOfAvailabilityCheck: mode = null`, t => {
+  t.plan(11);
+
+  quickCompare(t, true,  {mode: 'null', from: 'truthy string'});
+  quickCompare(t, true,  {mode: 'null', from: 123});
+  quickCompare(t, true,  {mode: 'null', from: true});
+
+  quickCompare(t, true,  {mode: 'null', from: ''});
+  quickCompare(t, true,  {mode: 'null', from: 0});
+  quickCompare(t, true,  {mode: 'null', from: -1});
+  quickCompare(t, true,  {mode: 'null', from: false});
+
+  quickCompare(t, true,  {mode: 'null', from: [1, 2, 3]});
+  quickCompare(t, true,  {mode: 'null', from: []});
+
+  quickCompare(t, false, {mode: 'null', from: null});
+  quickCompare(t, false, {mode: 'null', from: undefined});
+});
+
+t.test(`withResultOfAvailabilityCheck: mode = empty`, t => {
+  t.plan(11);
+
+  quickThrows(t, {mode: 'empty', from: 'truthy string'});
+  quickThrows(t, {mode: 'empty', from: 123});
+  quickThrows(t, {mode: 'empty', from: true});
+
+  quickThrows(t, {mode: 'empty', from: ''});
+  quickThrows(t, {mode: 'empty', from: 0});
+  quickThrows(t, {mode: 'empty', from: -1});
+  quickThrows(t, {mode: 'empty', from: false});
+
+  quickCompare(t, true,  {mode: 'empty', from: [1, 2, 3]});
+  quickCompare(t, false, {mode: 'empty', from: []});
+
+  quickCompare(t, false, {mode: 'empty', from: null});
+  quickCompare(t, false, {mode: 'empty', from: undefined});
+});
+
+t.test(`withResultOfAvailabilityCheck: mode = falsy`, t => {
+  t.plan(11);
+
+  quickCompare(t, true,  {mode: 'falsy', from: 'truthy string'});
+  quickCompare(t, true,  {mode: 'falsy', from: 123});
+  quickCompare(t, true,  {mode: 'falsy', from: true});
+
+  quickCompare(t, false, {mode: 'falsy', from: ''});
+  quickCompare(t, false, {mode: 'falsy', from: 0});
+  quickCompare(t, true,  {mode: 'falsy', from: -1});
+  quickCompare(t, false, {mode: 'falsy', from: false});
+
+  quickCompare(t, true,  {mode: 'falsy', from: [1, 2, 3]});
+  quickCompare(t, false, {mode: 'falsy', from: []});
+
+  quickCompare(t, false, {mode: 'falsy', from: null});
+  quickCompare(t, false, {mode: 'falsy', from: undefined});
+});
+
+t.test(`withResultOfAvailabilityCheck: mode = index`, t => {
+  t.plan(11);
+
+  quickCompare(t, false, {mode: 'index', from: 'truthy string'});
+  quickCompare(t, true,  {mode: 'index', from: 123});
+  quickCompare(t, false, {mode: 'index', from: true});
+
+  quickCompare(t, false, {mode: 'index', from: ''});
+  quickCompare(t, true,  {mode: 'index', from: 0});
+  quickCompare(t, false, {mode: 'index', from: -1});
+  quickCompare(t, false, {mode: 'index', from: false});
+
+  quickCompare(t, false, {mode: 'index', from: [1, 2, 3]});
+  quickCompare(t, false, {mode: 'index', from: []});
+
+  quickCompare(t, false, {mode: 'index', from: null});
+  quickCompare(t, false, {mode: 'index', from: undefined});
+});
+
+t.test(`withResultOfAvailabilityCheck: default mode`, t => {
+  t.plan(1);
+
+  const template = withResultOfAvailabilityCheck({
+    from: 'foo',
+  });
+
+  t.match(template.toDescription(), {
+    inputMapping: {
+      from: input.dependency('foo'),
+      mode: input.value('null'),
+    },
+  });
+});
+
+t.test(`withResultOfAvailabilityCheck: validate static inputs`, t => {
+  t.plan(5);
+
+  t.throws(
+    () => withResultOfAvailabilityCheck({}),
+    {message: `Errors in input options passed to withResultOfAvailabilityCheck`, errors: [
+      {message: `Required these inputs: from`},
+    ]});
+
+  t.doesNotThrow(() =>
+    withResultOfAvailabilityCheck({
+      from: 'dependency1',
+      mode: 'dependency2',
+    }));
+
+  t.doesNotThrow(() =>
+    withResultOfAvailabilityCheck({
+      from: input.value('some static value'),
+      mode: input.value('null'),
+    }));
+
+  t.throws(
+    () => withResultOfAvailabilityCheck({
+      from: 'foo',
+      mode: input.value('invalid'),
+    }),
+    {message: `Errors in input options passed to withResultOfAvailabilityCheck`, errors: [
+      {message: `mode: Expected one of null empty falsy index, got invalid`},
+    ]});
+
+  t.throws(() =>
+    withResultOfAvailabilityCheck({
+      from: input.value(null),
+      mode: input.value(null),
+    }),
+    {message: `Errors in input options passed to withResultOfAvailabilityCheck`, errors: [
+      {message: `mode: Expected a value, got null`},
+    ]});
+});
+
+t.test(`withResultOfAvailabilityCheck: validate dynamic inputs`, t => {
+  t.plan(2);
+
+  t.throws(
+    () => composite.expose.compute({
+      from: 'apple',
+      mode: 'banana',
+    }),
+    {message: `Error computing composition`, cause:
+      {message: `Error computing composition withResultOfAvailabilityCheck`, cause:
+        {message: `Errors in input values provided to withResultOfAvailabilityCheck`, errors: [
+          {message: `mode: Expected one of null empty falsy index, got banana`},
+        ]}}});
+
+  t.throws(
+    () => composite.expose.compute({
+      from: null,
+      mode: null,
+    }),
+    {message: `Error computing composition`, cause:
+      {message: `Error computing composition withResultOfAvailabilityCheck`, cause:
+        {message: `Errors in input values provided to withResultOfAvailabilityCheck`, errors: [
+          {message: `mode: Expected a value, got null`},
+        ]}}});
+});
diff --git a/test/unit/data/composite/data/withPropertiesFromObject.js b/test/unit/data/composite/data/withPropertiesFromObject.js
new file mode 100644
index 0000000..750dc8c
--- /dev/null
+++ b/test/unit/data/composite/data/withPropertiesFromObject.js
@@ -0,0 +1,254 @@
+import t from 'tap';
+
+import {compositeFrom, input} from '#composite';
+import {exposeDependency} from '#composite/control-flow';
+import {withPropertiesFromObject} from '#composite/data';
+
+const composite = compositeFrom({
+  compose: false,
+
+  steps: [
+    withPropertiesFromObject({
+      object: 'object',
+      properties: 'properties',
+    }),
+
+    exposeDependency({dependency: '#object'}),
+  ],
+});
+
+t.test(`withPropertiesFromObject: basic behavior`, t => {
+  t.plan(4);
+
+  t.match(composite, {
+    expose: {
+      dependencies: ['object', 'properties'],
+    },
+  });
+
+  t.same(
+    composite.expose.compute({
+      object: {foo: 'bar', bim: 'BOOM', bam: 'baz'},
+      properties: ['foo', 'bim'],
+    }),
+    {foo: 'bar', bim: 'BOOM'});
+
+  t.same(
+    composite.expose.compute({
+      object: {value1: 'uwah', value2: 'arah'},
+      properties: ['value1', 'value3'],
+    }),
+    {value1: 'uwah', value3: null});
+
+  t.same(
+    composite.expose.compute({
+      object: null,
+      properties: ['ohMe', 'ohMy', 'ohDear'],
+    }),
+    {ohMe: null, ohMy: null, ohDear: null});
+});
+
+t.test(`withPropertiesFromObject: output shapes & values`, t => {
+  t.plan(2 * 2 * 3 ** 2);
+
+  const dependencies = {
+    ['object_dependency']:
+      {foo: 'apple', bar: 'banana', baz: 'orange'},
+    [input('object_neither')]:
+      {foo: 'koala', bar: 'okapi', baz: 'mongoose'},
+    ['properties_dependency']:
+      ['foo', 'bar', 'missing1'],
+    [input('properties_neither')]:
+      ['foo', 'baz', 'missing3'],
+  };
+
+  const mapLevel1 = [
+    [input.value('prefix_value'), [
+      ['object_dependency', [
+        ['properties_dependency', {
+          '#object': {foo: 'apple', bar: 'banana', missing1: null},
+        }],
+        [input.value(['bar', 'baz', 'missing2']), {
+          '#prefix_value.bar': 'banana',
+          '#prefix_value.baz': 'orange',
+          '#prefix_value.missing2': null,
+        }],
+        [input('properties_neither'), {
+          '#object': {foo: 'apple', baz: 'orange', missing3: null},
+        }]]],
+
+      [input.value({foo: 'ouh', bar: 'rah', baz: 'nyu'}), [
+        ['properties_dependency', {
+          '#object': {foo: 'ouh', bar: 'rah', missing1: null},
+        }],
+        [input.value(['bar', 'baz', 'missing2']), {
+          '#prefix_value.bar': 'rah',
+          '#prefix_value.baz': 'nyu',
+          '#prefix_value.missing2': null,
+        }],
+        [input('properties_neither'), {
+          '#object': {foo: 'ouh', baz: 'nyu', missing3: null},
+        }]]],
+
+      [input('object_neither'), [
+        ['properties_dependency', {
+          '#object': {foo: 'koala', bar: 'okapi', missing1: null},
+        }],
+        [input.value(['bar', 'baz', 'missing2']), {
+          '#prefix_value.bar': 'okapi',
+          '#prefix_value.baz': 'mongoose',
+          '#prefix_value.missing2': null,
+        }],
+        [input('properties_neither'), {
+          '#object': {foo: 'koala', baz: 'mongoose', missing3: null},
+        }]]]]],
+
+    [input.value(null), [
+      ['object_dependency', [
+        ['properties_dependency', {
+          '#object': {foo: 'apple', bar: 'banana', missing1: null},
+        }],
+        [input.value(['bar', 'baz', 'missing2']), {
+          '#object_dependency.bar': 'banana',
+          '#object_dependency.baz': 'orange',
+          '#object_dependency.missing2': null,
+        }],
+        [input('properties_neither'), {
+          '#object': {foo: 'apple', baz: 'orange', missing3: null},
+        }]]],
+
+      [input.value({foo: 'ouh', bar: 'rah', baz: 'nyu'}), [
+        ['properties_dependency', {
+          '#object': {foo: 'ouh', bar: 'rah', missing1: null},
+        }],
+        [input.value(['bar', 'baz', 'missing2']), {
+          '#object.bar': 'rah',
+          '#object.baz': 'nyu',
+          '#object.missing2': null,
+        }],
+        [input('properties_neither'), {
+          '#object': {foo: 'ouh', baz: 'nyu', missing3: null},
+        }]]],
+
+      [input('object_neither'), [
+        ['properties_dependency', {
+          '#object': {foo: 'koala', bar: 'okapi', missing1: null},
+        }],
+        [input.value(['bar', 'baz', 'missing2']), {
+          '#object.bar': 'okapi',
+          '#object.baz': 'mongoose',
+          '#object.missing2': null,
+        }],
+        [input('properties_neither'), {
+          '#object': {foo: 'koala', baz: 'mongoose', missing3: null},
+        }]]]]],
+  ];
+
+  for (const [prefixInput, mapLevel2] of mapLevel1) {
+    for (const [objectInput, mapLevel3] of mapLevel2) {
+      for (const [propertiesInput, outputDict] of mapLevel3) {
+        const step = withPropertiesFromObject({
+          prefix: prefixInput,
+          object: objectInput,
+          properties: propertiesInput,
+        });
+
+        quickCheckOutputs(step, outputDict);
+      }
+    }
+  }
+
+  function quickCheckOutputs(step, outputDict) {
+    t.same(
+      Object.keys(step.toDescription().outputs),
+      Object.keys(outputDict));
+
+    const composite = compositeFrom({
+      compose: false,
+      steps: [step, {
+        dependencies: Object.keys(outputDict),
+        compute: dependencies => dependencies,
+      }],
+    });
+
+    t.same(
+      composite.expose.compute(dependencies),
+      outputDict);
+  }
+});
+
+t.test(`withPropertiesFromObject: validate static inputs`, t => {
+  t.plan(3);
+
+  t.throws(
+    () => withPropertiesFromObject({}),
+    {message: `Errors in input options passed to withPropertiesFromObject`, errors: [
+      {message: `Required these inputs: object, properties`},
+    ]});
+
+  t.throws(
+    () => withPropertiesFromObject({
+      object: input.value('intriguing'),
+      properties: input.value('very'),
+      prefix: input.value({yes: 'yup'}),
+    }),
+    {message: `Errors in input options passed to withPropertiesFromObject`, errors: [
+      {message: `object: Expected an object, got string`},
+      {message: `properties: Expected an array, got string`},
+      {message: `prefix: Expected a string, got object`},
+    ]});
+
+  t.throws(
+    () => withPropertiesFromObject({
+      object: input.value([['abc', 1], ['def', 2], [123, 3]]),
+      properties: input.value(['abc', 'def', 123]),
+    }),
+    {message: `Errors in input options passed to withPropertiesFromObject`, errors: [
+      {message: `object: Expected an object, got array`},
+      {message: `properties: Errors validating array items`, errors: [
+        {
+          [Symbol.for('hsmusic.annotateError.indexInSourceArray')]: 2,
+          message: `Error at zero-index 2: 123`,
+          cause: {
+            message: `Expected a string, got number`,
+          },
+        },
+      ]},
+    ]});
+});
+
+t.test(`withPropertiesFromObject: validate dynamic inputs`, t => {
+  t.plan(2);
+
+  t.throws(
+    () => composite.expose.compute({
+      object: 'intriguing',
+      properties: 'onceMore',
+    }),
+    {message: `Error computing composition`, cause:
+      {message: `Error computing composition withPropertiesFromObject`, cause:
+        {message: `Errors in input values provided to withPropertiesFromObject`, errors: [
+          {message: `object: Expected an object, got string`},
+          {message: `properties: Expected an array, got string`},
+        ]}}});
+
+  t.throws(
+    () => composite.expose.compute({
+      object: [['abc', 1], ['def', 2], [123, 3]],
+      properties: ['abc', 'def', 123],
+    }),
+    {message: `Error computing composition`, cause:
+      {message: `Error computing composition withPropertiesFromObject`, cause:
+        {message: `Errors in input values provided to withPropertiesFromObject`, errors: [
+          {message: `object: Expected an object, got array`},
+          {message: `properties: Errors validating array items`, errors: [
+            {
+              [Symbol.for('hsmusic.annotateError.indexInSourceArray')]: 2,
+              message: `Error at zero-index 2: 123`,
+              cause: {
+                message: `Expected a string, got number`,
+              },
+            },
+          ]},
+        ]}}});
+});
diff --git a/test/unit/data/composite/data/withPropertyFromObject.js b/test/unit/data/composite/data/withPropertyFromObject.js
new file mode 100644
index 0000000..6a772c3
--- /dev/null
+++ b/test/unit/data/composite/data/withPropertyFromObject.js
@@ -0,0 +1,122 @@
+import t from 'tap';
+
+import {compositeFrom, input} from '#composite';
+import {exposeDependency} from '#composite/control-flow';
+import {withPropertyFromObject} from '#composite/data';
+
+t.test(`withPropertyFromObject: basic behavior`, t => {
+  t.plan(4);
+
+  const composite = compositeFrom({
+    compose: false,
+
+    steps: [
+      withPropertyFromObject({
+        object: 'object',
+        property: 'property',
+      }),
+
+      exposeDependency({dependency: '#value'}),
+    ],
+  });
+
+  t.match(composite, {
+    expose: {
+      dependencies: ['object', 'property'],
+    },
+  });
+
+  t.equal(composite.expose.compute({
+    object: {foo: 'bar', bim: 'BOOM'},
+    property: 'bim',
+  }), 'BOOM');
+
+  t.equal(composite.expose.compute({
+    object: {value1: 'uwah'},
+    property: 'value2',
+  }), null);
+
+  t.equal(composite.expose.compute({
+    object: null,
+    property: 'oml where did me object go',
+  }), null);
+});
+
+t.test(`withPropertyFromObject: output shapes & values`, t => {
+  t.plan(2 * 3 ** 2);
+
+  const dependencies = {
+    ['object_dependency']:
+      {foo: 'apple', bar: 'banana', baz: 'orange'},
+    [input('object_neither')]:
+      {foo: 'koala', bar: 'okapi', baz: 'mongoose'},
+    ['property_dependency']:
+      'foo',
+    [input('property_neither')]:
+      'baz',
+  };
+
+  const mapLevel1 = [
+    ['object_dependency', [
+      ['property_dependency', {
+        '#value': 'apple',
+      }],
+      [input.value('bar'), {
+        '#object_dependency.bar': 'banana',
+      }],
+      [input('property_neither'), {
+        '#value': 'orange',
+      }]]],
+
+    [input.value({foo: 'ouh', bar: 'rah', baz: 'nyu'}), [
+      ['property_dependency', {
+        '#value': 'ouh',
+      }],
+      [input.value('bar'), {
+        '#value': 'rah',
+      }],
+      [input('property_neither'), {
+        '#value': 'nyu',
+      }]]],
+
+    [input('object_neither'), [
+      ['property_dependency', {
+        '#value': 'koala',
+      }],
+      [input.value('bar'), {
+        '#value': 'okapi',
+      }],
+      [input('property_neither'), {
+        '#value': 'mongoose',
+      }]]],
+  ];
+
+  for (const [objectInput, mapLevel2] of mapLevel1) {
+    for (const [propertyInput, outputDict] of mapLevel2) {
+      const step = withPropertyFromObject({
+        object: objectInput,
+        property: propertyInput,
+      });
+
+      quickCheckOutputs(step, outputDict);
+    }
+  }
+
+  function quickCheckOutputs(step, outputDict) {
+    t.same(
+      Object.keys(step.toDescription().outputs),
+      Object.keys(outputDict));
+
+    const composite = compositeFrom({
+      compose: false,
+      steps: [step, {
+        dependencies: Object.keys(outputDict),
+        compute: dependencies => dependencies,
+      }],
+    });
+
+    t.same(
+      composite.expose.compute(dependencies),
+      outputDict);
+  }
+});
diff --git a/test/unit/data/composite/data/withUniqueItemsOnly.js b/test/unit/data/composite/data/withUniqueItemsOnly.js
new file mode 100644
index 0000000..965b14b
--- /dev/null
+++ b/test/unit/data/composite/data/withUniqueItemsOnly.js
@@ -0,0 +1,84 @@
+import t from 'tap';
+
+import {compositeFrom, input} from '#composite';
+import {exposeDependency} from '#composite/control-flow';
+import {withUniqueItemsOnly} from '#composite/data';
+
+t.test(`withUniqueItemsOnly: basic behavior`, t => {
+  t.plan(3);
+
+  const composite = compositeFrom({
+    compose: false,
+
+    steps: [
+      withUniqueItemsOnly({
+        list: 'list',
+      }),
+
+      exposeDependency({dependency: '#list'}),
+    ],
+  });
+
+  t.match(composite, {
+    expose: {
+      dependencies: ['list'],
+    },
+  });
+
+  t.same(composite.expose.compute({
+    list: ['apple', 'banana', 'banana', 'banana', 'apple', 'watermelon'],
+  }), ['apple', 'banana', 'watermelon']);
+
+  t.same(composite.expose.compute({
+    list: [],
+  }), []);
+});
+
+t.test(`withUniqueItemsOnly: output shapes & values`, t => {
+  t.plan(2 * 3 ** 1);
+
+  const dependencies = {
+    ['list_dependency']:
+      [1, 1, 2, 3, 3, 4, 'foo', false, false, 4],
+    [input('list_neither')]:
+      [8, 8, 7, 6, 6, 5, 'bar', true, true, 5],
+  };
+
+  const mapLevel1 = [
+    ['list_dependency', {
+      '#list_dependency': [1, 2, 3, 4, 'foo', false],
+    }],
+    [input.value([-1, -1, 'interesting', 'very', 'interesting']), {
+      '#uniqueItems': [-1, 'interesting', 'very'],
+    }],
+    [input('list_neither'), {
+      '#uniqueItems': [8, 7, 6, 5, 'bar', true],
+    }],
+  ];
+
+  for (const [listInput, outputDict] of mapLevel1) {
+    const step = withUniqueItemsOnly({
+      list: listInput,
+    });
+
+    quickCheckOutputs(step, outputDict);
+  }
+
+  function quickCheckOutputs(step, outputDict) {
+    t.same(
+      Object.keys(step.toDescription().outputs),
+      Object.keys(outputDict));
+
+    const composite = compositeFrom({
+      compose: false,
+      steps: [step, {
+        dependencies: Object.keys(outputDict),
+        compute: dependencies => dependencies,
+      }],
+    });
+
+    t.same(
+      composite.expose.compute(dependencies),
+      outputDict);
+  }
+});
diff --git a/test/unit/data/composite/things/track/withAlbum.js b/test/unit/data/composite/things/track/withAlbum.js
new file mode 100644
index 0000000..d822f31
--- /dev/null
+++ b/test/unit/data/composite/things/track/withAlbum.js
@@ -0,0 +1,91 @@
+import t from 'tap';
+
+import {compositeFrom, input} from '#composite';
+import {exposeConstant, exposeDependency} from '#composite/control-flow';
+import {withAlbum} from '#composite/things/track';
+
+t.test(`withAlbum: basic behavior`, t => {
+  t.plan(3);
+
+  const composite = compositeFrom({
+    compose: false,
+    steps: [
+      withAlbum(),
+      exposeDependency({dependency: '#album'}),
+    ],
+  });
+
+  t.match(composite, {
+    expose: {
+      dependencies: ['albumData', 'this'],
+    },
+  });
+
+  const fakeTrack1 = {directory: 'foo'};
+  const fakeTrack2 = {directory: 'bar'};
+  const fakeAlbum = {directory: 'baz', tracks: [fakeTrack1]};
+
+  t.equal(
+    composite.expose.compute({
+      albumData: [fakeAlbum],
+      this: fakeTrack1,
+    }),
+    fakeAlbum);
+
+  t.equal(
+    composite.expose.compute({
+      albumData: [fakeAlbum],
+      this: fakeTrack2,
+    }),
+    null);
+});
+
+t.test(`withAlbum: early exit conditions`, t => {
+  t.plan(4);
+
+  const composite = compositeFrom({
+    compose: false,
+    steps: [
+      withAlbum(),
+      exposeConstant({
+        value: input.value('bimbam'),
+      }),
+    ],
+  });
+
+  const fakeTrack1 = {directory: 'foo'};
+  const fakeTrack2 = {directory: 'bar'};
+  const fakeAlbum = {directory: 'baz', tracks: [fakeTrack1]};
+
+  t.equal(
+    composite.expose.compute({
+      albumData: [fakeAlbum],
+      this: fakeTrack1,
+    }),
+    'bimbam',
+    `does not early exit if albumData is present and contains the track`);
+
+  t.equal(
+    composite.expose.compute({
+      albumData: [fakeAlbum],
+      this: fakeTrack2,
+    }),
+    'bimbam',
+    `does not early exit if albumData is present and does not contain the track`);
+
+  t.equal(
+    composite.expose.compute({
+      albumData: [],
+      this: fakeTrack1,
+    }),
+    'bimbam',
+    `does not early exit if albumData is empty array`);
+
+  t.equal(
+    composite.expose.compute({
+      albumData: null,
+      this: fakeTrack1,
+    }),
+    null,
+    `early exits if albumData is null`);
+});
diff --git a/test/unit/data/composite/wiki-data/withParsedCommentaryEntries.js b/test/unit/data/composite/wiki-data/withParsedCommentaryEntries.js
new file mode 100644
index 0000000..babe4fa
--- /dev/null
+++ b/test/unit/data/composite/wiki-data/withParsedCommentaryEntries.js
@@ -0,0 +1,102 @@
+import t from 'tap';
+
+import {compositeFrom, input} from '#composite';
+import thingConstructors from '#things';
+
+import {exposeDependency} from '#composite/control-flow';
+import {withParsedCommentaryEntries} from '#composite/wiki-data';
+
+const {Artist} = thingConstructors;
+
+const composite = compositeFrom({
+  compose: false,
+
+  steps: [
+    withParsedCommentaryEntries({
+      from: 'from',
+    }),
+
+    exposeDependency({dependency: '#parsedCommentaryEntries'}),
+  ],
+});
+
+function stubArtist(artistName = `Test Artist`) {
+  const artist = new Artist();
+  artist.name = artistName;
+
+  return artist;
+}
+
+t.test(`withParsedCommentaryEntries: basic behavior`, t => {
+  t.plan(3);
+
+  const artist1 = stubArtist(`Mobius Trip`);
+  const artist2 = stubArtist(`Hadron Kaleido`);
+
+  const artistData = [artist1, artist2];
+
+  t.match(composite, {
+    expose: {
+      dependencies: ['from', 'artistData'],
+    },
+  });
+
+  t.same(composite.expose.compute({
+    artistData,
+    from:
+      `<i>Mobius Trip:</i>\n` +
+      `Some commentary.\n` +
+      `Very cool.\n`,
+  }), [
+    {
+      artists: [artist1],
+      artistDisplayText: null,
+      annotation: null,
+      date: null,
+      body: `Some commentary.\nVery cool.`,
+    },
+  ]);
+
+  t.same(composite.expose.compute({
+    artistData,
+    from:
+      `<i>Mobius Trip|Moo-bius Trip:</i> (music, art, 12 January 2015)\n` +
+      `First commentary entry.\n` +
+      `Very cool.\n` +
+      `<i>Hadron Kaleido|<b>[[artist:hadron-kaleido|The Ol' Hadron]]</b>:</i> (moral support, 4/4/2022)\n` +
+      `Second commentary entry. Yes. So cool.\n` +
+      `<i>Mystery Artist:</i> (pingas, August 25, 2023)\n` +
+      `Oh no.. Oh dear...\n` +
+      `<i>Mobius Trip, Hadron Kaleido:</i>\n` +
+      `And back around we go.`,
+  }), [
+    {
+      artists: [artist1],
+      artistDisplayText: `Moo-bius Trip`,
+      annotation: `music, art`,
+      date: new Date('12 January 2015'),
+      body: `First commentary entry.\nVery cool.`,
+    },
+    {
+      artists: [artist2],
+      artistDisplayText: `<b>[[artist:hadron-kaleido|The Ol' Hadron]]</b>`,
+      annotation: `moral support`,
+      date: new Date('4 April 2022'),
+      body: `Second commentary entry. Yes. So cool.`,
+    },
+    {
+      artists: [],
+      artistDisplayText: null,
+      annotation: `pingas`,
+      date: new Date('25 August 2023'),
+      body: `Oh no.. Oh dear...`,
+    },
+    {
+      artists: [artist1, artist2],
+      artistDisplayText: null,
+      annotation: null,
+      date: null,
+      body: `And back around we go.`,
+    },
+  ]);
+});
diff --git a/test/unit/data/compositeFrom.js b/test/unit/data/compositeFrom.js
new file mode 100644
index 0000000..0029667
--- /dev/null
+++ b/test/unit/data/compositeFrom.js
@@ -0,0 +1,345 @@
+import t from 'tap';
+
+import {compositeFrom, continuationSymbol, input} from '#composite';
+import {isString} from '#validators';
+
+t.test(`compositeFrom: basic behavior`, t => {
+  t.plan(2);
+
+  const composite = compositeFrom({
+    annotation: `myComposite`,
+    compose: false,
+
+    steps: [
+      {
+        dependencies: ['foo'],
+        compute: (continuation, {foo}) =>
+          continuation({'#bar': foo * 2}),
+      },
+
+      {
+        dependencies: ['#bar', 'baz', 'suffix'],
+        compute: ({'#bar': bar, baz, suffix}) =>
+          baz.repeat(bar) + suffix,
+      },
+    ],
+  });
+
+  t.match(composite, {
+    annotation: `myComposite`,
+
+    flags: {expose: true, compose: false, update: false},
+
+    expose: {
+      dependencies: ['foo', 'baz', 'suffix'],
+      compute: Function,
+      transform: null,
+    },
+
+    update: null,
+  });
+
+  t.equal(
+    composite.expose.compute({
+      foo: 3,
+      baz: 'ba',
+      suffix: 'BOOM',
+    }),
+    'babababababaBOOM');
+});
+
+t.test(`compositeFrom: input-shaped step dependencies`, t => {
+  t.plan(2);
+
+  const composite = compositeFrom({
+    compose: false,
+    steps: [
+      {
+        dependencies: [
+          input.myself(),
+          input.updateValue(),
+        ],
+
+        transform: (updateValue1, {
+          [input.myself()]: me,
+          [input.updateValue()]: updateValue2,
+        }) => ({me, updateValue1, updateValue2}),
+      },
+    ],
+  });
+
+  t.match(composite, {
+    expose: {
+      dependencies: ['this'],
+      transform: Function,
+      compute: null,
+    },
+  });
+
+  const myself = {foo: 'bar'};
+
+  t.same(
+    composite.expose.transform('banana', {
+      this: myself,
+      pomelo: 'delicious',
+    }),
+    {
+      me: myself,
+      updateValue1: 'banana',
+      updateValue2: 'banana',
+    });
+});
+
+t.test(`compositeFrom: dependencies from inputs`, t => {
+  t.plan(3);
+
+  const composite = compositeFrom({
+    annotation: `myComposite`,
+
+    compose: true,
+
+    inputMapping: {
+      foo:      input('bar'),
+      pomelo:   input.value('delicious'),
+      humorous: input.dependency('#mammal'),
+      data:     input.dependency('albumData'),
+      ref:      input.updateValue(),
+    },
+
+    inputDescriptions: {
+      foo:      input(),
+      pomelo:   input(),
+      humorous: input(),
+      data:     input(),
+      ref:      input(),
+    },
+
+    steps: [
+      {
+        dependencies: [
+          input('foo'),
+          input('pomelo'),
+          input('humorous'),
+          input('data'),
+          input('ref'),
+        ],
+
+        compute: (continuation, {
+          [input('foo')]: foo,
+          [input('pomelo')]: pomelo,
+          [input('humorous')]: humorous,
+          [input('data')]: data,
+          [input('ref')]: ref,
+        }) => continuation.exit({foo, pomelo, humorous, data, ref}),
+      },
+    ],
+  });
+
+  t.match(composite, {
+    expose: {
+      dependencies: [
+        input('bar'),
+        '#mammal',
+        'albumData',
+      ],
+
+      transform: Function,
+      compute: null,
+    },
+  });
+
+  const exitData = {};
+  const continuation = {
+    exit(value) {
+      Object.assign(exitData, value);
+      return continuationSymbol;
+    },
+  };
+
+  t.equal(
+    composite.expose.transform('album:bepis', continuation, {
+      [input('bar')]: 'squid time',
+      '#mammal': 'fox',
+      'albumData': ['album1', 'album2'],
+    }),
+    continuationSymbol);
+
+  t.same(exitData, {
+    foo: 'squid time',
+    pomelo: 'delicious',
+    humorous: 'fox',
+    data: ['album1', 'album2'],
+    ref: 'album:bepis',
+  });
+});
+
+t.test(`compositeFrom: update from various sources`, t => {
+  t.plan(3);
+
+  const match = {
+    flags: {update: true, expose: true, compose: false},
+
+    update: {
+      validate: isString,
+      default: 'foo',
+    },
+
+    expose: {
+      transform: Function,
+      compute: null,
+    },
+  };
+
+  t.test(`compositeFrom: update from composition description`, t => {
+    t.plan(2);
+
+    const composite = compositeFrom({
+      compose: false,
+
+      update: {
+        validate: isString,
+        default: 'foo',
+      },
+
+      steps: [
+        {transform: (value, continuation) => continuation(value.repeat(2))},
+        {transform: (value) => `Xx_${value}_xX`},
+      ],
+    });
+
+    t.match(composite, match);
+    t.equal(composite.expose.transform('foo'), `Xx_foofoo_xX`);
+  });
+
+  t.test(`compositeFrom: update from step dependencies`, t => {
+    t.plan(2);
+
+    const composite = compositeFrom({
+      compose: false,
+
+      steps: [
+        {
+          dependencies: [
+            input.updateValue({
+              validate: isString,
+              default: 'foo',
+            }),
+          ],
+
+          compute: ({
+            [input.updateValue()]: value,
+          }) => `Xx_${value.repeat(2)}_xX`,
+        },
+      ],
+    });
+
+    t.match(composite, match);
+    t.equal(composite.expose.transform('foo'), 'Xx_foofoo_xX');
+  });
+
+  t.test(`compositeFrom: update from inputs`, t => {
+    t.plan(3);
+
+    const composite = compositeFrom({
+      inputMapping: {
+        myInput: input.updateValue({
+          validate: isString,
+          default: 'foo',
+        }),
+      },
+
+      inputDescriptions: {
+        myInput: input(),
+      },
+
+      steps: [
+        {
+          dependencies: [input('myInput')],
+          compute: (continuation, {
+            [input('myInput')]: value,
+          }) => continuation({
+            '#value': `Xx_${value.repeat(2)}_xX`,
+          }),
+        },
+
+        {
+          dependencies: ['#value'],
+          transform: (_value, continuation, {'#value': value}) =>
+            continuation(value),
+        },
+      ],
+    });
+
+    let continuationValue = null;
+    const continuation = value => {
+      continuationValue = value;
+      return continuationSymbol;
+    };
+
+    t.match(composite, {
+      ...match,
+
+      flags: {update: true, expose: true, compose: true},
+    });
+
+    t.equal(
+      composite.expose.transform('foo', continuation),
+      continuationSymbol);
+
+    t.equal(continuationValue, 'Xx_foofoo_xX');
+  });
+});
+
+t.test(`compositeFrom: dynamic input validation from type`, t => {
+  t.plan(2);
+
+  const composite = compositeFrom({
+    inputMapping: {
+      string:   input('string'),
+      number:   input('number'),
+      boolean:  input('boolean'),
+      function: input('function'),
+      object:   input('object'),
+      array:    input('array'),
+    },
+
+    inputDescriptions: {
+      string:   input({null: true, type: 'string'}),
+      number:   input({null: true, type: 'number'}),
+      boolean:  input({null: true, type: 'boolean'}),
+      function: input({null: true, type: 'function'}),
+      object:   input({null: true, type: 'object'}),
+      array:    input({null: true, type: 'array'}),
+    },
+
+    outputs: {'#result': '#result'},
+
+    steps: [
+      {compute: continuation => continuation({'#result': 'OK'})},
+    ],
+  });
+
+  const notCalledSymbol = Symbol('continuation not called');
+
+  let continuationValue;
+  const continuation = value => {
+    continuationValue = value;
+    return continuationSymbol;
+  };
+
+  let thrownError;
+
+  try {
+    continuationValue = notCalledSymbol;
+    thrownError = null;
+    composite.expose.compute(continuation, {
+      [input('string')]: 123,
+    });
+  } catch (error) {
+    thrownError = error;
+  }
+
+  t.equal(continuationValue, notCalledSymbol);
+  t.match(thrownError, {
+  });
+});
diff --git a/test/unit/data/templateCompositeFrom.js b/test/unit/data/templateCompositeFrom.js
new file mode 100644
index 0000000..2de1873
--- /dev/null
+++ b/test/unit/data/templateCompositeFrom.js
@@ -0,0 +1,209 @@
+import t from 'tap';
+
+import {isString} from '#validators';
+
+import {
+  compositeFrom,
+  continuationSymbol,
+  input,
+  templateCompositeFrom,
+} from '#composite';
+
+t.test(`templateCompositeFrom: basic behavior`, t => {
+  t.plan(1);
+
+  const myCoolUtility = templateCompositeFrom({
+    annotation: `myCoolUtility`,
+
+    inputs: {
+      foo: input(),
+    },
+
+    outputs: ['#bar'],
+
+    steps: () => [
+      {
+        dependencies: [input('foo')],
+        compute: (continuation, {
+          [input('foo')]: foo,
+        }) => continuation({
+          ['#bar']: (typeof foo).toUpperCase()
+        }),
+      },
+    ],
+  });
+
+  const instantiatedTemplate = myCoolUtility({
+    foo: 'color',
+  });
+
+  t.match(instantiatedTemplate.toDescription(), {
+    annotation: `myCoolUtility`,
+
+    inputMapping: {
+      foo: input.dependency('color'),
+    },
+
+    inputDescriptions: {
+      foo: input(),
+    },
+
+    outputs: {
+      '#bar': '#bar',
+    },
+
+    steps: Function,
+  });
+});
+
+t.test(`templateCompositeFrom: validate static input values`, t => {
+  t.plan(3);
+
+  const stub = {
+    annotation: 'stubComposite',
+    outputs: ['#result'],
+    steps: () => [{compute: continuation => continuation({'#result': 'OK'})}],
+  };
+
+  const quickThrows = (t, composite, inputOptions, ...errorMessages) =>
+    t.throws(
+      () => composite(inputOptions),
+      {
+        message: `Errors in input options passed to stubComposite`,
+        errors: errorMessages.map(message => ({message})),
+      });
+
+  t.test(`templateCompositeFrom: validate input token shapes`, t => {
+    t.plan(15);
+
+    const template1 = templateCompositeFrom({
+      ...stub, inputs: {
+        foo: input(),
+      },
+    });
+
+    t.doesNotThrow(
+      () => template1({foo: 'dependency'}));
+
+    t.doesNotThrow(
+      () => template1({foo: input.dependency('dependency')}));
+
+    t.doesNotThrow(
+      () => template1({foo: input.value('static value')}));
+
+    t.doesNotThrow(
+      () => template1({foo: input('outerInput')}));
+
+    t.doesNotThrow(
+      () => template1({foo: input.updateValue()}));
+
+    t.doesNotThrow(
+      () => template1({foo: input.myself()}));
+
+    quickThrows(t, template1,
+      {foo: input.staticValue()},
+      `foo: Expected dependency name or value-providing input() call, got input.staticValue`);
+
+    quickThrows(t, template1,
+      {foo: input.staticDependency()},
+      `foo: Expected dependency name or value-providing input() call, got input.staticDependency`);
+
+    const template2 = templateCompositeFrom({
+      ...stub, inputs: {
+        bar: input.staticDependency(),
+      },
+    });
+
+    t.doesNotThrow(
+      () => template2({bar: 'dependency'}));
+
+    t.doesNotThrow(
+      () => template2({bar: input.dependency('dependency')}));
+
+    quickThrows(t, template2,
+      {bar: input.value(123)},
+      `bar: Expected dependency name, got input.value`);
+
+    quickThrows(t, template2,
+      {bar: input('outOfPlace')},
+      `bar: Expected dependency name, got input`);
+
+    const template3 = templateCompositeFrom({
+      ...stub, inputs: {
+        baz: input.staticValue(),
+      },
+    });
+
+    t.doesNotThrow(
+      () => template3({baz: input.value(1025)}));
+
+    quickThrows(t, template3,
+      {baz: 'dependency'},
+      `baz: Expected input.value() call, got dependency name`);
+
+    quickThrows(t, template3,
+      {baz: input('outOfPlace')},
+      `baz: Expected input.value() call, got input() call`);
+  });
+
+  t.test(`templateCompositeFrom: validate missing / misplaced inputs`, t => {
+    t.plan(1);
+
+    const template = templateCompositeFrom({
+      ...stub, inputs: {
+        foo: input(),
+        bar: input(),
+      },
+    });
+
+    t.throws(
+      () => template({
+        baz: 'aeiou',
+        raz: input.value(123),
+      }),
+      {message: `Errors in input options passed to stubComposite`, errors: [
+        {message: `Unexpected input names: baz, raz`},
+        {message: `Required these inputs: foo, bar`},
+      ]});
+  });
+
+  t.test(`templateCompositeFrom: validate acceptsNull / defaultValue: null`, t => {
+    t.plan(3);
+
+    const template1 = templateCompositeFrom({
+      ...stub, inputs: {
+        foo: input(),
+      },
+    });
+
+    t.throws(
+      () => template1({}),
+      {message: `Errors in input options passed to stubComposite`, errors: [
+        {message: `Required these inputs: foo`},
+      ]},
+      `throws if input missing and not marked specially`);
+
+    const template2 = templateCompositeFrom({
+      ...stub, inputs: {
+        bar: input({acceptsNull: true}),
+      },
+    });
+
+    t.throws(
+      () => template2({}),
+      {message: `Errors in input options passed to stubComposite`, errors: [
+        {message: `Required these inputs: bar`},
+      ]},
+      `throws if input missing even if marked {acceptsNull}`);
+
+    const template3 = templateCompositeFrom({
+      ...stub, inputs: {
+        baz: input({defaultValue: null}),
+      },
+    });
+
+    t.doesNotThrow(
+      () => template3({}),
+      `does not throw if input missing if marked {defaultValue: null}`);
+  });
+});
diff --git a/test/unit/data/things/album.js b/test/unit/data/things/album.js
new file mode 100644
index 0000000..46ea83b
--- /dev/null
+++ b/test/unit/data/things/album.js
@@ -0,0 +1,451 @@
+import t from 'tap';
+
+import {linkAndBindWikiData} from '#test-lib';
+import thingConstructors from '#things';
+
+const {
+  Album,
+  ArtTag,
+  Artist,
+  Track,
+} = thingConstructors;
+
+function stubArtTag(tagName = `Test Art Tag`) {
+  const tag = new ArtTag();
+  tag.name = tagName;
+
+  return tag;
+}
+
+function stubArtistAndContribs() {
+  const artist = new Artist();
+  artist.name = `Test Artist`;
+
+  const contribs = [{who: `Test Artist`, what: null}];
+  const badContribs = [{who: `Figment of Your Imagination`, what: null}];
+
+  return {artist, contribs, badContribs};
+}
+
+function stubTrack(directory = 'foo') {
+  const track = new Track();
+  track.directory = directory;
+
+  return track;
+}
+
+t.test(`Album.artTags`, t => {
+  t.plan(3);
+
+  const {artist, contribs} = stubArtistAndContribs();
+  const album = new Album();
+  const tag1 = stubArtTag(`Tag 1`);
+  const tag2 = stubArtTag(`Tag 2`);
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+    artTagData: [tag1, tag2],
+  });
+
+  t.same(album.artTags, [],
+    `artTags #1: defaults to empty array`);
+
+  album.artTags = [`Tag 1`, `Tag 2`];
+
+  t.same(album.artTags, [],
+    `artTags #2: is empty if album doesn't have cover artists`);
+
+  album.coverArtistContribs = contribs;
+
+  t.same(album.artTags, [tag1, tag2],
+    `artTags #3: resolves if album has cover artists`);
+});
+
+t.test(`Album.bannerDimensions`, t => {
+  t.plan(4);
+
+  const album = new Album();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+  });
+
+  t.equal(album.bannerDimensions, null,
+    `Album.bannerDimensions #1: defaults to null`);
+
+  album.bannerDimensions = [1200, 275];
+
+  t.equal(album.bannerDimensions, null,
+    `Album.bannerDimensions #2: is null if bannerArtistContribs empty`);
+
+  album.bannerArtistContribs = badContribs;
+
+  t.equal(album.bannerDimensions, null,
+    `Album.bannerDimensions #3: is null if bannerArtistContribs resolves empty`);
+
+  album.bannerArtistContribs = contribs;
+
+  t.same(album.bannerDimensions, [1200, 275],
+    `Album.bannerDimensions #4: is own value`);
+});
+
+t.test(`Album.bannerFileExtension`, t => {
+  t.plan(5);
+
+  const album = new Album();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+  });
+
+  t.equal(album.bannerFileExtension, null,
+    `Album.bannerFileExtension #1: defaults to null`);
+
+  album.bannerFileExtension = 'png';
+
+  t.equal(album.bannerFileExtension, null,
+    `Album.bannerFileExtension #2: is null if bannerArtistContribs empty`);
+
+  album.bannerArtistContribs = badContribs;
+
+  t.equal(album.bannerFileExtension, null,
+    `Album.bannerFileExtension #3: is null if bannerArtistContribs resolves empty`);
+
+  album.bannerArtistContribs = contribs;
+
+  t.equal(album.bannerFileExtension, 'png',
+    `Album.bannerFileExtension #4: is own value`);
+
+  album.bannerFileExtension = null;
+
+  t.equal(album.bannerFileExtension, 'jpg',
+    `Album.bannerFileExtension #5: defaults to jpg`);
+});
+
+t.test(`Album.bannerStyle`, t => {
+  t.plan(4);
+
+  const album = new Album();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+  });
+
+  t.equal(album.bannerStyle, null,
+    `Album.bannerStyle #1: defaults to null`);
+
+  album.bannerStyle = `opacity: 0.5`;
+
+  t.equal(album.bannerStyle, null,
+    `Album.bannerStyle #2: is null if bannerArtistContribs empty`);
+
+  album.bannerArtistContribs = badContribs;
+
+  t.equal(album.bannerStyle, null,
+    `Album.bannerStyle #3: is null if bannerArtistContribs resolves empty`);
+
+  album.bannerArtistContribs = contribs;
+
+  t.equal(album.bannerStyle, `opacity: 0.5`,
+    `Album.bannerStyle #4: is own value`);
+});
+
+t.test(`Album.coverArtDate`, t => {
+  t.plan(6);
+
+  const album = new Album();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+  });
+
+  t.equal(album.coverArtDate, null,
+    `Album.coverArtDate #1: defaults to null`);
+
+  album.date = new Date('2012-10-25');
+
+  t.equal(album.coverArtDate, null,
+    `Album.coverArtDate #2: is null if coverArtistContribs empty (1/2)`);
+
+  album.coverArtDate = new Date('2011-04-13');
+
+  t.equal(album.coverArtDate, null,
+    `Album.coverArtDate #3: is null if coverArtistContribs empty (2/2)`);
+
+  album.coverArtistContribs = contribs;
+
+  t.same(album.coverArtDate, new Date('2011-04-13'),
+    `Album.coverArtDate #4: is own value`);
+
+  album.coverArtDate = null;
+
+  t.same(album.coverArtDate, new Date(`2012-10-25`),
+    `Album.coverArtDate #5: inherits album release date`);
+
+  album.coverArtistContribs = badContribs;
+
+  t.equal(album.coverArtDate, null,
+    `Album.coverArtDate #6: is null if coverArtistContribs resolves empty`);
+});
+
+t.test(`Album.coverArtFileExtension`, t => {
+  t.plan(5);
+
+  const album = new Album();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+  });
+
+  t.equal(album.coverArtFileExtension, null,
+    `Album.coverArtFileExtension #1: is null if coverArtistContribs empty (1/2)`);
+
+  album.coverArtFileExtension = 'png';
+
+  t.equal(album.coverArtFileExtension, null,
+    `Album.coverArtFileExtension #2: is null if coverArtistContribs empty (2/2)`);
+
+  album.coverArtFileExtension = null;
+  album.coverArtistContribs = contribs;
+
+  t.equal(album.coverArtFileExtension, 'jpg',
+    `Album.coverArtFileExtension #3: defaults to jpg`);
+
+  album.coverArtFileExtension = 'png';
+
+  t.equal(album.coverArtFileExtension, 'png',
+    `Album.coverArtFileExtension #4: is own value`);
+
+  album.coverArtistContribs = badContribs;
+
+  t.equal(album.coverArtFileExtension, null,
+    `Album.coverArtFileExtension #5: is null if coverArtistContribs resolves empty`);
+});
+
+t.test(`Album.tracks`, t => {
+  t.plan(5);
+
+  const album = new Album();
+  const track1 = stubTrack('track1');
+  const track2 = stubTrack('track2');
+  const track3 = stubTrack('track3');
+  const tracks = [track1, track2, track3];
+
+  album.ownTrackData = tracks;
+
+  for (const track of tracks) {
+    track.albumData = [album];
+  }
+
+  t.same(album.tracks, [],
+    `Album.tracks #1: defaults to empty array`);
+
+  album.trackSections = [
+    {tracks: ['track:track1', 'track:track2', 'track:track3']},
+  ];
+
+  t.same(album.tracks, [track1, track2, track3],
+    `Album.tracks #2: pulls tracks from one track section`);
+
+  album.trackSections = [
+    {tracks: ['track:track1']},
+    {tracks: ['track:track2', 'track:track3']},
+  ];
+
+  t.same(album.tracks, [track1, track2, track3],
+    `Album.tracks #3: pulls tracks from multiple track sections`);
+
+  album.trackSections = [
+    {tracks: ['track:track1', 'track:does-not-exist']},
+    {tracks: ['track:this-one-neither', 'track:track2']},
+    {tracks: ['track:effectively-empty-section']},
+    {tracks: ['track:track3']},
+  ];
+
+  t.same(album.tracks, [track1, track2, track3],
+    `Album.tracks #4: filters out references without matches`);
+
+  album.trackSections = [
+    {tracks: ['track:track1']},
+    {},
+    {tracks: ['track:track2']},
+    {},
+    {},
+    {tracks: ['track:track3']},
+  ];
+
+  t.same(album.tracks, [track1, track2, track3],
+    `Album.tracks #5: skips missing tracks property`);
+});
+
+t.test(`Album.trackSections`, t => {
+  t.plan(7);
+
+  const album = new Album();
+  const track1 = stubTrack('track1');
+  const track2 = stubTrack('track2');
+  const track3 = stubTrack('track3');
+  const track4 = stubTrack('track4');
+  const tracks = [track1, track2, track3, track4];
+
+  album.ownTrackData = tracks;
+
+  for (const track of tracks) {
+    track.albumData = [album];
+  }
+
+  album.trackSections = [
+    {tracks: ['track:track1', 'track:track2']},
+    {tracks: ['track:track3', 'track:track4']},
+  ];
+
+  t.match(album.trackSections, [
+    {tracks: [track1, track2]},
+    {tracks: [track3, track4]},
+  ], `Album.trackSections #1: exposes tracks`);
+
+  t.match(album.trackSections, [
+    {tracks: [track1, track2], startIndex: 0},
+    {tracks: [track3, track4], startIndex: 2},
+  ], `Album.trackSections #2: exposes startIndex`);
+
+  album.trackSections = [
+    {name: 'First section', tracks: ['track:track1']},
+    {name: 'Second section', tracks: ['track:track2']},
+    {tracks: ['track:track3']},
+  ];
+
+  t.match(album.trackSections, [
+    {name: 'First section', tracks: [track1]},
+    {name: 'Second section', tracks: [track2]},
+    {name: 'Unnamed Track Section', tracks: [track3]},
+  ], `Album.trackSections #3: exposes name, with fallback value`);
+
+  album.color = '#123456';
+
+  album.trackSections = [
+    {tracks: ['track:track1'], color: null},
+    {tracks: ['track:track2'], color: '#abcdef'},
+    {tracks: ['track:track3'], color: null},
+  ];
+
+  t.match(album.trackSections, [
+    {tracks: [track1], color: '#123456'},
+    {tracks: [track2], color: '#abcdef'},
+    {tracks: [track3], color: '#123456'},
+  ], `Album.trackSections #4: exposes color, inherited from album`);
+
+  album.trackSections = [
+    {tracks: ['track:track1'], dateOriginallyReleased: null},
+    {tracks: ['track:track2'], dateOriginallyReleased: new Date('2009-04-11')},
+    {tracks: ['track:track3'], dateOriginallyReleased: null},
+  ];
+
+  t.match(album.trackSections, [
+    {tracks: [track1], dateOriginallyReleased: null},
+    {tracks: [track2], dateOriginallyReleased: new Date('2009-04-11')},
+    {tracks: [track3], dateOriginallyReleased: null},
+  ], `Album.trackSections #5: exposes dateOriginallyReleased, if present`);
+
+  album.trackSections = [
+    {tracks: ['track:track1'], isDefaultTrackSection: true},
+    {tracks: ['track:track2'], isDefaultTrackSection: false},
+    {tracks: ['track:track3'], isDefaultTrackSection: null},
+  ];
+
+  t.match(album.trackSections, [
+    {tracks: [track1], isDefaultTrackSection: true},
+    {tracks: [track2], isDefaultTrackSection: false},
+    {tracks: [track3], isDefaultTrackSection: false},
+  ], `Album.trackSections #6: exposes isDefaultTrackSection, defaults to false`);
+
+  album.trackSections = [
+    {tracks: ['track:track1', 'track:track2', 'track:snooping'], color: '#112233'},
+    {tracks: ['track:track3', 'track:as-usual'],                 color: '#334455'},
+    {tracks: [],                                                 color: '#bbbbba'},
+    {tracks: ['track:icy', 'track:chilly', 'track:frigid'],      color: '#556677'},
+    {tracks: ['track:track4'],                                   color: '#778899'},
+  ];
+
+  t.match(album.trackSections, [
+    {tracks: [track1, track2], color: '#112233'},
+    {tracks: [track3],         color: '#334455'},
+    {tracks: [track4],         color: '#778899'},
+  ], `Album.trackSections #7: filters out references without matches & empty sections`);
+});
+
+t.test(`Album.wallpaperFileExtension`, t => {
+  t.plan(5);
+
+  const album = new Album();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+  });
+
+  t.equal(album.wallpaperFileExtension, null,
+    `Album.wallpaperFileExtension #1: defaults to null`);
+
+  album.wallpaperFileExtension = 'png';
+
+  t.equal(album.wallpaperFileExtension, null,
+    `Album.wallpaperFileExtension #2: is null if wallpaperArtistContribs empty`);
+
+  album.wallpaperArtistContribs = contribs;
+
+  t.equal(album.wallpaperFileExtension, 'png',
+    `Album.wallpaperFileExtension #3: is own value`);
+
+  album.wallpaperFileExtension = null;
+
+  t.equal(album.wallpaperFileExtension, 'jpg',
+    `Album.wallpaperFileExtension #4: defaults to jpg`);
+
+  album.wallpaperArtistContribs = badContribs;
+
+  t.equal(album.wallpaperFileExtension, null,
+    `Album.wallpaperFileExtension #5: is null if wallpaperArtistContribs resolves empty`);
+});
+
+t.test(`Album.wallpaperStyle`, t => {
+  t.plan(4);
+
+  const album = new Album();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+  });
+
+  t.equal(album.wallpaperStyle, null,
+    `Album.wallpaperStyle #1: defaults to null`);
+
+  album.wallpaperStyle = `opacity: 0.5`;
+
+  t.equal(album.wallpaperStyle, null,
+    `Album.wallpaperStyle #2: is null if wallpaperArtistContribs empty`);
+
+  album.wallpaperArtistContribs = badContribs;
+
+  t.equal(album.wallpaperStyle, null,
+    `Album.wallpaperStyle #3: is null if wallpaperArtistContribs resolves empty`);
+
+  album.wallpaperArtistContribs = contribs;
+
+  t.equal(album.wallpaperStyle, `opacity: 0.5`,
+    `Album.wallpaperStyle #4: is own value`);
+});
diff --git a/test/unit/data/things/art-tag.js b/test/unit/data/things/art-tag.js
new file mode 100644
index 0000000..561c93e
--- /dev/null
+++ b/test/unit/data/things/art-tag.js
@@ -0,0 +1,71 @@
+import t from 'tap';
+
+import {linkAndBindWikiData} from '#test-lib';
+import thingConstructors from '#things';
+
+const {
+  Album,
+  Artist,
+  ArtTag,
+  Track,
+} = thingConstructors;
+
+function stubAlbum(tracks, directory = 'bar') {
+  const album = new Album();
+  album.directory = directory;
+
+  const trackRefs = tracks.map(t => Thing.getReference(t));
+  album.trackSections = [{tracks: trackRefs}];
+
+  return album;
+}
+
+function stubTrack(directory = 'foo') {
+  const track = new Track();
+  track.directory = directory;
+
+  return track;
+}
+
+function stubTrackAndAlbum(trackDirectory = 'foo', albumDirectory = 'bar') {
+  const track = stubTrack(trackDirectory);
+  const album = stubAlbum([track], albumDirectory);
+
+  return {track, album};
+}
+
+function stubArtist(artistName = `Test Artist`) {
+  const artist = new Artist();
+  artist.name = artistName;
+
+  return artist;
+}
+
+function stubArtistAndContribs(artistName = `Test Artist`) {
+  const artist = stubArtist(artistName);
+  const contribs = [{who: artistName, what: null}];
+  const badContribs = [{who: `Figment of Your Imagination`, what: null}];
+
+  return {artist, contribs, badContribs};
+}
+
+t.test(`ArtTag.nameShort`, t => {
+  t.plan(3);
+
+  const artTag = new ArtTag();
+
+  artTag.name = `Dave Strider`;
+
+  t.equal(artTag.nameShort, `Dave Strider`,
+    `ArtTag #1: defaults to name`);
+
+  artTag.name = `Dave Strider (Homestuck)`;
+
+  t.equal(artTag.nameShort, `Dave Strider`,
+    `ArtTag #2: trims parenthical part at end`);
+
+  artTag.name = `This (And) That (Then)`;
+
+  t.equal(artTag.nameShort, `This (And) That`,
+    `ArtTag #2: doesn't trim midlde parenthical part`);
+});
diff --git a/test/unit/data/things/flash.js b/test/unit/data/things/flash.js
new file mode 100644
index 0000000..6205960
--- /dev/null
+++ b/test/unit/data/things/flash.js
@@ -0,0 +1,55 @@
+import t from 'tap';
+
+import {linkAndBindWikiData} from '#test-lib';
+import thingConstructors from '#things';
+
+const {
+  Flash,
+  FlashAct,
+  Thing,
+} = thingConstructors;
+
+function stubFlash(directory = 'foo') {
+  const flash = new Flash();
+  flash.directory = directory;
+
+  return flash;
+}
+
+function stubFlashAct(flashes, directory = 'bar') {
+  const flashAct = new FlashAct();
+  flashAct.directory = directory;
+  flashAct.flashes = flashes.map(flash => Thing.getReference(flash));
+
+  return flashAct;
+}
+
+t.test(`Flash.color`, t => {
+  t.plan(4);
+
+  const flash = stubFlash();
+  const flashAct = stubFlashAct([flash]);
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    flashData: [flash],
+    flashActData: [flashAct],
+  });
+
+  t.equal(flash.color, null,
+    `color #1: defaults to null`);
+
+  flashAct.color = '#abcdef';
+  XXX_decacheWikiData();
+
+  t.equal(flash.color, '#abcdef',
+    `color #2: inherits from flash act`);
+
+  flash.color = '#123456';
+
+  t.equal(flash.color, '#123456',
+    `color #3: is own value`);
+
+  t.throws(() => { flash.color = '#aeiouw'; },
+    {cause: TypeError},
+    `color #4: must be set to valid color`);
+});
diff --git a/test/unit/data/things/track.js b/test/unit/data/things/track.js
new file mode 100644
index 0000000..b1c1611
--- /dev/null
+++ b/test/unit/data/things/track.js
@@ -0,0 +1,759 @@
+import t from 'tap';
+
+import {linkAndBindWikiData} from '#test-lib';
+import thingConstructors from '#things';
+
+const {
+  Album,
+  ArtTag,
+  Artist,
+  Flash,
+  FlashAct,
+  Thing,
+  Track,
+} = thingConstructors;
+
+function stubAlbum(tracks, directory = 'bar') {
+  const album = new Album();
+  album.directory = directory;
+
+  const trackRefs = tracks.map(t => Thing.getReference(t));
+  album.trackSections = [{tracks: trackRefs}];
+
+  return album;
+}
+
+function stubTrack(directory = 'foo') {
+  const track = new Track();
+  track.directory = directory;
+
+  return track;
+}
+
+function stubTrackAndAlbum(trackDirectory = 'foo', albumDirectory = 'bar') {
+  const track = stubTrack(trackDirectory);
+  const album = stubAlbum([track], albumDirectory);
+
+  return {track, album};
+}
+
+function stubArtist(artistName = `Test Artist`) {
+  const artist = new Artist();
+  artist.name = artistName;
+
+  return artist;
+}
+
+function stubArtistAndContribs(artistName = `Test Artist`) {
+  const artist = stubArtist(artistName);
+  const contribs = [{who: artistName, what: null}];
+  const badContribs = [{who: `Figment of Your Imagination`, what: null}];
+
+  return {artist, contribs, badContribs};
+}
+
+function stubArtTag(tagName = `Test Art Tag`) {
+  const tag = new ArtTag();
+  tag.name = tagName;
+
+  return tag;
+}
+
+function stubFlashAndAct(directory = 'zam') {
+  const flash = new Flash();
+  flash.directory = directory;
+
+  const flashAct = new FlashAct();
+  flashAct.flashes = [Thing.getReference(flash)];
+
+  return {flash, flashAct};
+}
+
+t.test(`Track.album`, t => {
+  t.plan(6);
+
+  // Note: These asserts use manual albumData/trackData relationships
+  // to illustrate more specifically the properties which are expected to
+  // be relevant for this case. Other properties use the same underlying
+  // get-album behavior as Track.album so aren't tested as aggressively.
+
+  const track1 = stubTrack('track1');
+  const track2 = stubTrack('track2');
+  const album1 = new Album();
+  const album2 = new Album();
+
+  t.equal(track1.album, null,
+    `album #1: defaults to null`);
+
+  track1.albumData = [album1, album2];
+  track2.albumData = [album1, album2];
+  album1.ownTrackData = [track1, track2];
+  album2.ownTrackData = [track1, track2];
+  album1.trackSections = [{tracks: ['track:track1']}];
+  album2.trackSections = [{tracks: ['track:track2']}];
+
+  t.equal(track1.album, album1,
+    `album #2: is album when album's trackSections matches track`);
+
+  track1.albumData = [album2, album1];
+
+  t.equal(track1.album, album1,
+    `album #3: is album when albumData is in different order`);
+
+  track1.albumData = [];
+
+  t.equal(track1.album, null,
+    `album #4: is null when track missing albumData`);
+
+  album1.ownTrackData = [];
+  track1.albumData = [album1, album2];
+
+  t.equal(track1.album, null,
+    `album #5: is null when album missing ownTrackData`);
+
+  album1.ownTrackData = [track1, track2];
+  album1.trackSections = [{tracks: ['track:track2']}];
+
+  // XXX_decacheWikiData
+  track1.albumData = [];
+  track1.albumData = [album1, album2];
+
+  t.equal(track1.album, null,
+    `album #6: is null when album's trackSections don't match track`);
+});
+
+t.test(`Track.artTags`, t => {
+  t.plan(6);
+
+  const {track, album} = stubTrackAndAlbum();
+  const {artist, contribs} = stubArtistAndContribs();
+  const tag1 = stubArtTag(`Tag 1`);
+  const tag2 = stubArtTag(`Tag 2`);
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+    artTagData: [tag1, tag2],
+    trackData: [track],
+  });
+
+  t.same(track.artTags, [],
+    `artTags #1: defaults to empty array`);
+
+  track.artTags = [`Tag 1`, `Tag 2`];
+
+  t.same(track.artTags, [],
+    `artTags #2: is empty if track doesn't have cover artists`);
+
+  track.coverArtistContribs = contribs;
+
+  t.same(track.artTags, [tag1, tag2],
+    `artTags #3: resolves if track has cover artists`);
+
+  track.coverArtistContribs = null;
+  album.trackCoverArtistContribs = contribs;
+
+  XXX_decacheWikiData();
+
+  t.same(track.artTags, [tag1, tag2],
+    `artTags #4: resolves if track inherits cover artists`);
+
+  track.disableUniqueCoverArt = true;
+
+  t.same(track.artTags, [],
+    `artTags #5: is empty if track disables unique cover artwork`);
+
+  album.coverArtistContribs = contribs;
+  album.artTags = [`Tag 2`];
+
+  XXX_decacheWikiData();
+
+  t.notSame(track.artTags, [tag2],
+    `artTags #6: doesn't inherit from album's art tags`);
+});
+
+t.test(`Track.artistContribs`, t => {
+  t.plan(4);
+
+  const {track, album} = stubTrackAndAlbum();
+  const artist1 = stubArtist(`Artist 1`);
+  const artist2 = stubArtist(`Artist 2`);
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist1, artist2],
+    trackData: [track],
+  });
+
+  t.same(track.artistContribs, [],
+    `artistContribs #1: defaults to empty array`);
+
+  album.artistContribs = [
+    {who: `Artist 1`, what: `composition`},
+    {who: `Artist 2`, what: null},
+  ];
+
+  XXX_decacheWikiData();
+
+  t.same(track.artistContribs,
+    [{who: artist1, what: `composition`}, {who: artist2, what: null}],
+    `artistContribs #2: inherits album artistContribs`);
+
+  track.artistContribs = [
+    {who: `Artist 1`, what: `arrangement`},
+  ];
+
+  t.same(track.artistContribs, [{who: artist1, what: `arrangement`}],
+    `artistContribs #3: resolves from own value`);
+
+  track.artistContribs = [
+    {who: `Artist 1`, what: `snooping`},
+    {who: `Artist 413`, what: `as`},
+    {who: `Artist 2`, what: `usual`},
+  ];
+
+  t.same(track.artistContribs,
+    [{who: artist1, what: `snooping`}, {who: artist2, what: `usual`}],
+    `artistContribs #4: filters out names without matches`);
+});
+
+t.test(`Track.color`, t => {
+  t.plan(5);
+
+  const {track, album} = stubTrackAndAlbum();
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    trackData: [track],
+  });
+
+  t.equal(track.color, null,
+    `color #1: defaults to null`);
+
+  album.color = '#abcdef';
+  album.trackSections = [{
+    color: '#beeeef',
+    tracks: [Thing.getReference(track)],
+  }];
+  XXX_decacheWikiData();
+
+  t.equal(track.color, '#beeeef',
+    `color #2: inherits from track section before album`);
+
+  // Replace the album with a completely fake one. This isn't realistic, since
+  // in correct data, Album.tracks depends on Albums.trackSections and so the
+  // track's album will always have a corresponding track section. But if that
+  // connection breaks for some future reason (with the album still present),
+  // Track.color should still inherit directly from the album.
+  track.albumData = [
+    {
+      constructor: {[Thing.referenceType]: 'album'},
+      color: '#abcdef',
+      tracks: [track],
+      trackSections: [
+        {color: '#baaaad', tracks: []},
+      ],
+    },
+  ];
+
+  t.equal(track.color, '#abcdef',
+    `color #3: inherits from album without matching track section`);
+
+  track.color = '#123456';
+
+  t.equal(track.color, '#123456',
+    `color #4: is own value`);
+
+  t.throws(() => { track.color = '#aeiouw'; },
+    {cause: TypeError},
+    `color #5: must be set to valid color`);
+});
+
+t.test(`Track.commentatorArtists`, t => {
+  t.plan(8);
+
+  const track = new Track();
+  const artist1 = stubArtist(`SnooPING`);
+  const artist2 = stubArtist(`ASUsual`);
+  const artist3 = stubArtist(`Icy`);
+
+  linkAndBindWikiData({
+    trackData: [track],
+    artistData: [artist1, artist2, artist3],
+  });
+
+  // Keep track of the last commentary string in a separate value, since
+  // the track.commentary property exposes as a completely different format
+  // (i.e. an array of objects, one for each entry), and so isn't compatible
+  // with the += operator on its own.
+  let commentary;
+
+  track.commentary = commentary =
+    `<i>SnooPING:</i>\n` +
+    `Wow.\n`;
+
+  t.same(track.commentatorArtists, [artist1],
+    `Track.commentatorArtists #1: works with one commentator`);
+
+  track.commentary = commentary +=
+    `<i>ASUsual:</i>\n` +
+    `Yes!\n`;
+
+  t.same(track.commentatorArtists, [artist1, artist2],
+    `Track.commentatorArtists #2: works with two commentators`);
+
+  track.commentary = commentary +=
+    `<i>Icy|<b>Icy What You Did There</b>:</i>\n` +
+    `Incredible.\n`;
+
+  t.same(track.commentatorArtists, [artist1, artist2, artist3],
+    `Track.commentatorArtists #3: works with custom artist text`);
+
+  track.commentary = commentary =
+    `<i>Icy:</i> (project manager)\n` +
+    `Very good track.\n`;
+
+  t.same(track.commentatorArtists, [artist3],
+    `Track.commentatorArtists #4: works with annotation`);
+
+  track.commentary = commentary =
+    `<i>Icy:</i> (project manager, 08/15/2023)\n` +
+    `Very very good track.\n`;
+
+  t.same(track.commentatorArtists, [artist3],
+    `Track.commentatorArtists #5: works with date`);
+
+  track.commentary = commentary +=
+    `<i>Ohohohoho:</i>\n` +
+    `OHOHOHOHOHOHO...\n`;
+
+  t.same(track.commentatorArtists, [artist3],
+    `Track.commentatorArtists #6: ignores artist names not found`);
+
+  track.commentary = commentary +=
+    `<i>Icy:</i>\n` +
+    `I'm back!\n`;
+
+  t.same(track.commentatorArtists, [artist3],
+    `Track.commentatorArtists #7: ignores duplicate artist`);
+
+  track.commentary = commentary +=
+    `<i>SNooPING, ASUsual, Icy:</i>\n` +
+    `WITH ALL THREE POWERS COMBINED...`;
+
+  t.same(track.commentatorArtists, [artist3, artist1, artist2],
+    `Track.commentatorArtists #8: works with more than one artist in one entry`);
+});
+
+t.test(`Track.coverArtistContribs`, t => {
+  t.plan(5);
+
+  const {track, album} = stubTrackAndAlbum();
+  const artist1 = stubArtist(`Artist 1`);
+  const artist2 = stubArtist(`Artist 2`);
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist1, artist2],
+    trackData: [track],
+  });
+
+  t.same(track.coverArtistContribs, [],
+    `coverArtistContribs #1: defaults to empty array`);
+
+  album.trackCoverArtistContribs = [
+    {who: `Artist 1`, what: `lines`},
+    {who: `Artist 2`, what: null},
+  ];
+
+  XXX_decacheWikiData();
+
+  t.same(track.coverArtistContribs,
+    [{who: artist1, what: `lines`}, {who: artist2, what: null}],
+    `coverArtistContribs #2: inherits album trackCoverArtistContribs`);
+
+  track.coverArtistContribs = [
+    {who: `Artist 1`, what: `collage`},
+  ];
+
+  t.same(track.coverArtistContribs, [{who: artist1, what: `collage`}],
+    `coverArtistContribs #3: resolves from own value`);
+
+  track.coverArtistContribs = [
+    {who: `Artist 1`, what: `snooping`},
+    {who: `Artist 413`, what: `as`},
+    {who: `Artist 2`, what: `usual`},
+  ];
+
+  t.same(track.coverArtistContribs,
+    [{who: artist1, what: `snooping`}, {who: artist2, what: `usual`}],
+    `coverArtistContribs #4: filters out names without matches`);
+
+  track.disableUniqueCoverArt = true;
+
+  t.same(track.coverArtistContribs, [],
+    `coverArtistContribs #5: is empty if track disables unique cover artwork`);
+});
+
+t.test(`Track.coverArtDate`, t => {
+  t.plan(8);
+
+  const {track, album} = stubTrackAndAlbum();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+    trackData: [track],
+  });
+
+  track.coverArtistContribs = contribs;
+
+  t.equal(track.coverArtDate, null,
+    `coverArtDate #1: defaults to null`);
+
+  album.trackArtDate = new Date('2012-12-12');
+
+  XXX_decacheWikiData();
+
+  t.same(track.coverArtDate, new Date('2012-12-12'),
+    `coverArtDate #2: inherits album trackArtDate`);
+
+  track.coverArtDate = new Date('2009-09-09');
+
+  t.same(track.coverArtDate, new Date('2009-09-09'),
+    `coverArtDate #3: is own value`);
+
+  track.coverArtistContribs = [];
+
+  t.equal(track.coverArtDate, null,
+    `coverArtDate #4: is null if track coverArtistContribs empty`);
+
+  album.trackCoverArtistContribs = contribs;
+
+  XXX_decacheWikiData();
+
+  t.same(track.coverArtDate, new Date('2009-09-09'),
+    `coverArtDate #5: is not null if album trackCoverArtistContribs specified`);
+
+  album.trackCoverArtistContribs = badContribs;
+
+  XXX_decacheWikiData();
+
+  t.equal(track.coverArtDate, null,
+    `coverArtDate #6: is null if album trackCoverArtistContribs resolves empty`);
+
+  track.coverArtistContribs = badContribs;
+
+  t.equal(track.coverArtDate, null,
+    `coverArtDate #7: is null if track coverArtistContribs resolves empty`);
+
+  track.coverArtistContribs = contribs;
+  track.disableUniqueCoverArt = true;
+
+  t.equal(track.coverArtDate, null,
+    `coverArtDate #8: is null if track disables unique cover artwork`);
+});
+
+t.test(`Track.coverArtFileExtension`, t => {
+  t.plan(8);
+
+  const {track, album} = stubTrackAndAlbum();
+  const {artist, contribs} = stubArtistAndContribs();
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+    trackData: [track],
+  });
+
+  t.equal(track.coverArtFileExtension, null,
+    `coverArtFileExtension #1: defaults to null`);
+
+  track.coverArtistContribs = contribs;
+
+  t.equal(track.coverArtFileExtension, 'jpg',
+    `coverArtFileExtension #2: is jpg if has cover art and not further specified`);
+
+  track.coverArtistContribs = [];
+
+  album.coverArtistContribs = contribs;
+  XXX_decacheWikiData();
+
+  t.equal(track.coverArtFileExtension, null,
+    `coverArtFileExtension #3: only has value for unique cover art`);
+
+  track.coverArtistContribs = contribs;
+
+  album.trackCoverArtFileExtension = 'png';
+  XXX_decacheWikiData();
+
+  t.equal(track.coverArtFileExtension, 'png',
+    `coverArtFileExtension #4: inherits album trackCoverArtFileExtension (1/2)`);
+
+  track.coverArtFileExtension = 'gif';
+
+  t.equal(track.coverArtFileExtension, 'gif',
+    `coverArtFileExtension #5: is own value (1/2)`);
+
+  track.coverArtistContribs = [];
+
+  album.trackCoverArtistContribs = contribs;
+  XXX_decacheWikiData();
+
+  t.equal(track.coverArtFileExtension, 'gif',
+    `coverArtFileExtension #6: is own value (2/2)`);
+
+  track.coverArtFileExtension = null;
+
+  t.equal(track.coverArtFileExtension, 'png',
+    `coverArtFileExtension #7: inherits album trackCoverArtFileExtension (2/2)`);
+
+  track.disableUniqueCoverArt = true;
+
+  t.equal(track.coverArtFileExtension, null,
+    `coverArtFileExtension #8: is null if track disables unique cover art`);
+});
+
+t.test(`Track.date`, t => {
+  t.plan(3);
+
+  const {track, album} = stubTrackAndAlbum();
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    trackData: [track],
+  });
+
+  t.equal(track.date, null,
+    `date #1: defaults to null`);
+
+  album.date = new Date('2012-12-12');
+  XXX_decacheWikiData();
+
+  t.same(track.date, album.date,
+    `date #2: inherits from album`);
+
+  track.dateFirstReleased = new Date('2009-09-09');
+
+  t.same(track.date, new Date('2009-09-09'),
+    `date #3: is own dateFirstReleased`);
+});
+
+t.test(`Track.featuredInFlashes`, t => {
+  t.plan(2);
+
+  const {track, album} = stubTrackAndAlbum('track1');
+
+  const {flash: flash1, flashAct: flashAct1} = stubFlashAndAct('flash1');
+  const {flash: flash2, flashAct: flashAct2} = stubFlashAndAct('flash2');
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    trackData: [track],
+    flashData: [flash1, flash2],
+    flashActData: [flashAct1, flashAct2],
+  });
+
+  t.same(track.featuredInFlashes, [],
+    `featuredInFlashes #1: defaults to empty array`);
+
+  flash1.featuredTracks = ['track:track1'];
+  flash2.featuredTracks = ['track:track1'];
+  XXX_decacheWikiData();
+
+  t.same(track.featuredInFlashes, [flash1, flash2],
+    `featuredInFlashes #2: matches flashes' featuredTracks`);
+});
+
+t.test(`Track.hasUniqueCoverArt`, t => {
+  t.plan(7);
+
+  const {track, album} = stubTrackAndAlbum();
+  const {artist, contribs, badContribs} = stubArtistAndContribs();
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album],
+    artistData: [artist],
+    trackData: [track],
+  });
+
+  t.equal(track.hasUniqueCoverArt, false,
+    `hasUniqueCoverArt #1: defaults to false`);
+
+  album.trackCoverArtistContribs = contribs;
+  XXX_decacheWikiData();
+
+  t.equal(track.hasUniqueCoverArt, true,
+    `hasUniqueCoverArt #2: is true if album specifies trackCoverArtistContribs`);
+
+  track.disableUniqueCoverArt = true;
+
+  t.equal(track.hasUniqueCoverArt, false,
+    `hasUniqueCoverArt #3: is false if disableUniqueCoverArt is true (1/2)`);
+
+  track.disableUniqueCoverArt = false;
+
+  album.trackCoverArtistContribs = badContribs;
+  XXX_decacheWikiData();
+
+  t.equal(track.hasUniqueCoverArt, false,
+    `hasUniqueCoverArt #4: is false if album's trackCoverArtistContribs resolve empty`);
+
+  track.coverArtistContribs = contribs;
+
+  t.equal(track.hasUniqueCoverArt, true,
+    `hasUniqueCoverArt #5: is true if track specifies coverArtistContribs`);
+
+  track.disableUniqueCoverArt = true;
+
+  t.equal(track.hasUniqueCoverArt, false,
+    `hasUniqueCoverArt #6: is false if disableUniqueCoverArt is true (2/2)`);
+
+  track.disableUniqueCoverArt = false;
+
+  track.coverArtistContribs = badContribs;
+
+  t.equal(track.hasUniqueCoverArt, false,
+    `hasUniqueCoverArt #7: is false if track's coverArtistContribs resolve empty`);
+});
+
+t.test(`Track.originalReleaseTrack`, t => {
+  t.plan(3);
+
+  const {track: track1, album: album1} = stubTrackAndAlbum('track1');
+  const {track: track2, album: album2} = stubTrackAndAlbum('track2');
+
+  const {wikiData, linkWikiDataArrays, XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album1, album2],
+    trackData: [track1, track2],
+  });
+
+  t.equal(track2.originalReleaseTrack, null,
+    `originalReleaseTrack #1: defaults to null`);
+
+  track2.originalReleaseTrack = 'track:track1';
+
+  t.equal(track2.originalReleaseTrack, track1,
+    `originalReleaseTrack #2: is resolved from own value`);
+
+  track2.trackData = [];
+
+  t.equal(track2.originalReleaseTrack, null,
+    `originalReleaseTrack #3: is null when track missing trackData`);
+});
+
+t.test(`Track.otherReleases`, t => {
+  t.plan(6);
+
+  const {track: track1, album: album1} = stubTrackAndAlbum('track1');
+  const {track: track2, album: album2} = stubTrackAndAlbum('track2');
+  const {track: track3, album: album3} = stubTrackAndAlbum('track3');
+  const {track: track4, album: album4} = stubTrackAndAlbum('track4');
+
+  const {wikiData, linkWikiDataArrays, XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album1, album2, album3, album4],
+    trackData: [track1, track2, track3, track4],
+  });
+
+  t.same(track1.otherReleases, [],
+    `otherReleases #1: defaults to empty array`);
+
+  track2.originalReleaseTrack = 'track:track1';
+  track3.originalReleaseTrack = 'track:track1';
+  track4.originalReleaseTrack = 'track:track1';
+  XXX_decacheWikiData();
+
+  t.same(track1.otherReleases, [track2, track3, track4],
+    `otherReleases #2: otherReleases of original release are its rereleases`);
+
+  wikiData.trackData = [track1, track3, track2, track4];
+  linkWikiDataArrays();
+
+  t.same(track1.otherReleases, [track3, track2, track4],
+    `otherReleases #3: otherReleases matches trackData order`);
+
+  wikiData.trackData = [track3, track2, track1, track4];
+  linkWikiDataArrays();
+
+  t.same(track2.otherReleases, [track1, track3, track4],
+    `otherReleases #4: otherReleases of rerelease are original track then other rereleases (1/3)`);
+
+  t.same(track3.otherReleases, [track1, track2, track4],
+    `otherReleases #5: otherReleases of rerelease are original track then other rereleases (2/3)`);
+
+  t.same(track4.otherReleases, [track1, track3, track2],
+    `otherReleases #6: otherReleases of rerelease are original track then other rereleases (3/3)`);
+});
+
+t.test(`Track.referencedByTracks`, t => {
+  t.plan(4);
+
+  const {track: track1, album: album1} = stubTrackAndAlbum('track1');
+  const {track: track2, album: album2} = stubTrackAndAlbum('track2');
+  const {track: track3, album: album3} = stubTrackAndAlbum('track3');
+  const {track: track4, album: album4} = stubTrackAndAlbum('track4');
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album1, album2, album3, album4],
+    trackData: [track1, track2, track3, track4],
+  });
+
+  t.same(track1.referencedByTracks, [],
+    `referencedByTracks #1: defaults to empty array`);
+
+  track2.referencedTracks = ['track:track1'];
+  track3.referencedTracks = ['track:track1'];
+  XXX_decacheWikiData();
+
+  t.same(track1.referencedByTracks, [track2, track3],
+    `referencedByTracks #2: matches tracks' referencedTracks`);
+
+  track4.sampledTracks = ['track:track1'];
+  XXX_decacheWikiData();
+
+  t.same(track1.referencedByTracks, [track2, track3],
+    `referencedByTracks #3: doesn't match tracks' sampledTracks`);
+
+  track3.originalReleaseTrack = 'track:track2';
+  XXX_decacheWikiData();
+
+  t.same(track1.referencedByTracks, [track2],
+    `referencedByTracks #4: doesn't include rereleases`);
+});
+
+t.test(`Track.sampledByTracks`, t => {
+  t.plan(4);
+
+  const {track: track1, album: album1} = stubTrackAndAlbum('track1');
+  const {track: track2, album: album2} = stubTrackAndAlbum('track2');
+  const {track: track3, album: album3} = stubTrackAndAlbum('track3');
+  const {track: track4, album: album4} = stubTrackAndAlbum('track4');
+
+  const {XXX_decacheWikiData} = linkAndBindWikiData({
+    albumData: [album1, album2, album3, album4],
+    trackData: [track1, track2, track3, track4],
+  });
+
+  t.same(track1.sampledByTracks, [],
+    `sampledByTracks #1: defaults to empty array`);
+
+  track2.sampledTracks = ['track:track1'];
+  track3.sampledTracks = ['track:track1'];
+  XXX_decacheWikiData();
+
+  t.same(track1.sampledByTracks, [track2, track3],
+    `sampledByTracks #2: matches tracks' sampledTracks`);
+
+  track4.referencedTracks = ['track:track1'];
+  XXX_decacheWikiData();
+
+  t.same(track1.sampledByTracks, [track2, track3],
+    `sampledByTracks #3: doesn't match tracks' referencedTracks`);
+
+  track3.originalReleaseTrack = 'track:track2';
+  XXX_decacheWikiData();
+
+  t.same(track1.sampledByTracks, [track2],
+    `sampledByTracks #4: doesn't include rereleases`);
+});
diff --git a/test/unit/data/things/validators.js b/test/unit/data/things/validators.js
new file mode 100644
index 0000000..11134a9
--- /dev/null
+++ b/test/unit/data/things/validators.js
@@ -0,0 +1,440 @@
+import t from 'tap';
+import {showAggregate} from '#sugar';
+
+import {
+  // Basic types
+  isBoolean,
+  isCountingNumber,
+  isDate,
+  isNumber,
+  isString,
+  isStringNonEmpty,
+
+  // Complex types
+  isArray,
+  isObject,
+  validateArrayItems,
+
+  // Wiki data
+  isColor,
+  isCommentary,
+  isContentString,
+  isContribution,
+  isContributionList,
+  isDimensions,
+  isDirectory,
+  isDuration,
+  isFileExtension,
+  isName,
+  isURL,
+  validateReference,
+  validateReferenceList,
+
+  // Compositional utilities
+  anyOf,
+} from '#validators';
+
+function test(t, msg, fn) {
+  t.test(msg, t => {
+    try {
+      fn(t);
+    } catch (error) {
+      if (error instanceof AggregateError) {
+        showAggregate(error);
+      }
+      throw error;
+    }
+  });
+}
+
+// Basic types
+
+test(t, 'isBoolean', t => {
+  t.plan(4);
+  t.ok(isBoolean(true));
+  t.ok(isBoolean(false));
+  t.throws(() => isBoolean(1), TypeError);
+  t.throws(() => isBoolean('yes'), TypeError);
+});
+
+test(t, 'isNumber', t => {
+  t.plan(6);
+  t.ok(isNumber(123));
+  t.ok(isNumber(0.05));
+  t.ok(isNumber(0));
+  t.ok(isNumber(-10));
+  t.throws(() => isNumber('413'), TypeError);
+  t.throws(() => isNumber(true), TypeError);
+});
+
+test(t, 'isCountingNumber', t => {
+  t.plan(6);
+  t.ok(isCountingNumber(3));
+  t.ok(isCountingNumber(1));
+  t.throws(() => isCountingNumber(1.75), TypeError);
+  t.throws(() => isCountingNumber(0), TypeError);
+  t.throws(() => isCountingNumber(-1), TypeError);
+  t.throws(() => isCountingNumber('612'), TypeError);
+});
+
+test(t, 'isString', t => {
+  t.plan(3);
+  t.ok(isString('hello!'));
+  t.ok(isString(''));
+  t.throws(() => isString(100), TypeError);
+});
+
+test(t, 'isStringNonEmpty', t => {
+  t.plan(4);
+  t.ok(isStringNonEmpty('hello!'));
+  t.throws(() => isStringNonEmpty(''), TypeError);
+  t.throws(() => isStringNonEmpty('     '), TypeError);
+  t.throws(() => isStringNonEmpty(100), TypeError);
+});
+
+// Complex types
+
+test(t, 'isArray', t => {
+  t.plan(3);
+  t.ok(isArray([]));
+  t.throws(() => isArray({}), TypeError);
+  t.throws(() => isArray('1, 2, 3'), TypeError);
+});
+
+test(t, 'isDate', t => {
+  t.plan(3);
+  t.ok(isDate(new Date('2023-03-27 09:24:15')));
+  t.throws(() => isDate(new Date(Infinity)), TypeError);
+  t.throws(() => isDimensions('2023-03-27 09:24:15'), TypeError);
+});
+
+test(t, 'isObject', t => {
+  t.plan(3);
+  t.ok(isObject({}));
+  t.ok(isObject([]));
+  t.throws(() => isObject(null), TypeError);
+});
+
+test(t, 'validateArrayItems', t => {
+  t.plan(9);
+
+  t.ok(validateArrayItems(isNumber)([3, 4, 5]));
+  t.ok(validateArrayItems(validateArrayItems(isNumber))([[3, 4], [4, 5], [6, 7]]));
+
+  let caughtError = null;
+  try {
+    validateArrayItems(isNumber)([10, 20, 'one hundred million consorts', 30]);
+  } catch (err) {
+    caughtError = err;
+  }
+
+  t.not(caughtError, null);
+  t.ok(caughtError instanceof AggregateError);
+  t.equal(caughtError.errors.length, 1);
+  t.ok(caughtError.errors[0] instanceof Error);
+  t.equal(caughtError.errors[0][Symbol.for('hsmusic.annotateError.indexInSourceArray')], 2);
+  t.not(caughtError.errors[0].cause, null);
+  t.ok(caughtError.errors[0].cause instanceof TypeError);
+});
+
+// Wiki data
+
+t.test('isColor', t => {
+  t.plan(9);
+  t.ok(isColor('#123'));
+  t.ok(isColor('#1234'));
+  t.ok(isColor('#112233'));
+  t.ok(isColor('#11223344'));
+  t.ok(isColor('#abcdef00'));
+  t.ok(isColor('#ABCDEF'));
+  t.throws(() => isColor('#ggg'), TypeError);
+  t.throws(() => isColor('red'), TypeError);
+  t.throws(() => isColor('hsl(150deg 30% 60%)'), TypeError);
+});
+
+t.test('isCommentary', t => {
+  t.plan(9);
+
+  // TODO: Test specific error messages.
+  t.ok(isCommentary(`<i>Toby Fox:</i>\ndogsong.mp3`));
+  t.ok(isCommentary(`<i>Toby Fox:</i> (music)\ndogsong.mp3`));
+  t.throws(() => isCommentary(`dogsong.mp3\n<i>Toby Fox:</i>\ndogsong.mp3`));
+  t.throws(() => isCommentary(`<i>Toby Fox:</i> dogsong.mp3`));
+  t.throws(() => isCommentary(`<i>Toby Fox:</i> (music) dogsong.mp3`));
+  t.throws(() => isCommentary(`<i>I Have Nothing To Say:</i>`));
+  t.throws(() => isCommentary(123));
+  t.throws(() => isCommentary(``));
+  t.throws(() => isCommentary(`Technically, ah, er:</i>\nCorrect`));
+});
+
+t.test('isContentString', t => {
+  t.plan(12);
+
+  t.ok(isContentString(`Hello, world!`));
+  t.ok(isContentString(`Hello...\nWorld!`));
+
+  const quickThrows = (string, description) =>
+    t.throws(() => isContentString(string), description);
+
+  quickThrows(
+    `Snooping\xa0as usual, I\xa0\xa0\xa0SEE.`,
+    Object.assign(
+      new AggregateError([
+        new AggregateError([
+          new TypeError(`Replace "\xa0" (non-breaking space) with " " (normal space) between "ing" and "as " (pos: 9)`),
+          new TypeError(`Replace "\xa0\xa0\xa0" (non-breaking space) with "   " (normal space) between ", I" and "SEE" (pos: 21)`),
+        ], `Illegal characters found in content string`),
+      ], `Errors validating content string`),
+      {[Symbol.for(`hsmusic.aggregate.translucent`)]: 'single'}));
+
+  quickThrows(
+    `Oh\u200bdear,\n` +
+    `Oh dear,\n` +
+    `oh-dear-oh-dear-oh\u200bdear.`,
+    new AggregateError([
+      new AggregateError([
+        new TypeError(`Delete "\u200b" (zero-width space) between "Oh" and "dea" (line: 1, col: 3)`),
+        new TypeError(`Delete "\u200b" (zero-width space) between "-oh" and "dea" (line: 3, col: 19)`),
+      ]),
+    ]));
+
+  quickThrows(
+    `Well the days start comin'\xa0\xa0\xa0\xa0\u200b\u200b\xa0\xa0\xa0\u200b\u200b\u200band they don't stop comin'`,
+    new AggregateError([
+      new AggregateError([
+        new TypeError(`Replace "\xa0\xa0\xa0\xa0" (non-breaking space) with "    " (normal space) after "in'" (pos: 27)`),
+        new TypeError(`Delete "\u200b\u200b" (zero-width space) (pos: 31)`),
+        new TypeError(`Replace "\xa0\xa0\xa0" (non-breaking space) with "   " (normal space) (pos: 33)`),
+        new TypeError(`Delete "\u200b\u200b\u200b" (zero-width space) before "and" (pos: 36)`),
+      ]),
+    ]));
+
+  quickThrows(
+    `It's go-\u200bin',\n` +
+    `\u200bIt's goin',\u200b\n` +
+    `\u200b\u200bIt's going!`,
+    new AggregateError([
+      new AggregateError([
+        new TypeError(`Delete "\u200b" (zero-width space) between "go-" and "in'" (line: 1, col: 9)`),
+        new TypeError(`Delete "\u200b" (zero-width space) before "It'" (line: 2, col: 1)`),
+        new TypeError(`Delete "\u200b" (zero-width space) after "n'," (line: 2, col: 13)`),
+        new TypeError(`Delete "\u200b\u200b" (zero-width space) before "It'" (line: 3, col: 1)`),
+      ]),
+    ]));
+
+  quickThrows(
+    `  Room at the start.`,
+    new AggregateError([
+      new AggregateError([
+        new TypeError(`Matched "  " at start`),
+      ], `Whitespace found at start or end`),
+    ]));
+
+  quickThrows(
+    `Room at the end.      `,
+    new AggregateError([
+      new AggregateError([
+        new TypeError(`Matched "      " at end`),
+      ], `Whitespace found at start or end`),
+    ]));
+
+  quickThrows(
+    `      Room on both sides. `,
+    new AggregateError([
+      new AggregateError([
+        new TypeError(`Matched "      " at start`),
+        new TypeError(`Matched " " at end`),
+      ], `Whitespace found at start or end`),
+    ]));
+
+  quickThrows(
+    `We're going multiline! \n` +
+    `That we are, aye.    \n` +
+    `      \n`,
+    `Yessir.`,
+    new AggregateError([
+      new AggregateError([
+        new TypeError(`Matched " " at end of line 1`),
+        new TypeError(`Matched "    " at end of line 2`),
+        new TypeError(`Matched "      " as all of line 3`),
+      ], `Whitespace found at end of line`),
+    ]));
+
+  t.doesNotThrow(() =>
+    isContentString(
+      `It's cool.\n` +
+      `  It's cool.\n` +
+      `    It's cool.\n` +
+      `      It's so cool.`));
+
+  t.doesNotThrow(() =>
+    isContentString(
+      `\n` +
+      `\n` +
+      `It's okay for\n` +
+      `blank lines\n` +
+      `\n` +
+      `just about anywhere.\n` +
+      ``));
+});
+
+t.test('isContribution', t => {
+  t.plan(4);
+  t.ok(isContribution({who: 'artist:toby-fox', what: 'Music'}));
+  t.ok(isContribution({who: 'Toby Fox'}));
+  t.throws(() => isContribution(({who: 'group:umspaf', what: 'Organizing'})),
+    {errors: /who/});
+  t.throws(() => isContribution(({who: 'artist:toby-fox', what: 123})),
+    {errors: /what/});
+});
+
+t.test('isContributionList', t => {
+  t.plan(4);
+  t.ok(isContributionList([{who: 'Beavis'}, {who: 'Butthead', what: 'Wrangling'}]));
+  t.ok(isContributionList([]));
+  t.throws(() => isContributionList(2));
+  t.throws(() => isContributionList(['Charlie', 'Woodstock']));
+});
+
+test(t, 'isDimensions', t => {
+  t.plan(6);
+  t.ok(isDimensions([1, 1]));
+  t.ok(isDimensions([50, 50]));
+  t.ok(isDimensions([5000, 1]));
+  t.throws(() => isDimensions([1]), TypeError);
+  t.throws(() => isDimensions([413, 612, 1025]), TypeError);
+  t.throws(() => isDimensions('800x200'), TypeError);
+});
+
+test(t, 'isDirectory', t => {
+  t.plan(6);
+  t.ok(isDirectory('savior-of-the-waking-world'));
+  t.ok(isDirectory('MeGaLoVania'));
+  t.ok(isDirectory('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'));
+  t.throws(() => isDirectory(123), TypeError);
+  t.throws(() => isDirectory(''), TypeError);
+  t.throws(() => isDirectory('troll saint nicholas and the quest for the holy pail'), TypeError);
+});
+
+test(t, 'isDuration', t => {
+  t.plan(5);
+  t.ok(isDuration(60));
+  t.ok(isDuration(0.02));
+  t.ok(isDuration(0));
+  t.throws(() => isDuration(-1), TypeError);
+  t.throws(() => isDuration('10:25'), TypeError);
+});
+
+test(t, 'isFileExtension', t => {
+  t.plan(6);
+  t.ok(isFileExtension('png'));
+  t.ok(isFileExtension('jpg'));
+  t.ok(isFileExtension('sub_loc'));
+  t.throws(() => isFileExtension(''), TypeError);
+  t.throws(() => isFileExtension('.jpg'), TypeError);
+  t.throws(() => isFileExtension('just an image bro!!!!'), TypeError);
+});
+
+t.test('isName', t => {
+  t.plan(4);
+  t.ok(isName('Dogz 2.0'));
+  t.ok(isName('album:this-track-is-only-named-thusly-to-give-niklink-a-headache'));
+  t.throws(() => isName(''));
+  t.throws(() => isName(612));
+});
+
+t.test('isURL', t => {
+  t.plan(4);
+  t.ok(isURL(`https://hsmusic.wiki/foo/bar/hi?baz=25#hash`));
+  t.throws(() => isURL(`/the/dog/zone/`));
+  t.throws(() => isURL(25));
+  t.throws(() => isURL(new URL(`https://hsmusic.wiki/perfectly/reasonable/`)));
+});
+
+test(t, 'validateReference', t => {
+  t.plan(16);
+
+  const typeless = validateReference();
+  const track = validateReference('track');
+  const album = validateReference('album');
+
+  t.ok(track('track:doctor'));
+  t.ok(track('track:MeGaLoVania'));
+  t.ok(track('Showtime (Imp Strife Mix)'));
+  t.throws(() => track('track:troll saint nic'), TypeError);
+  t.throws(() => track('track:'), TypeError);
+  t.throws(() => track('album:homestuck-vol-1'), TypeError);
+
+  t.ok(album('album:sburb'));
+  t.ok(album('album:the-wanderers'));
+  t.ok(album('Homestuck Vol. 8'));
+  t.throws(() => album('album:Hiveswap Friendsim'), TypeError);
+  t.throws(() => album('album:'), TypeError);
+  t.throws(() => album('track:showtime-piano-refrain'), TypeError);
+
+  t.ok(typeless('Hopes and Dreams'));
+  t.ok(typeless('track:snowdin-town'));
+  t.throws(() => typeless(''), TypeError);
+  t.throws(() => typeless('album:undertale-soundtrack'));
+});
+
+test(t, 'validateReferenceList', t => {
+  const track = validateReferenceList('track');
+  const artist = validateReferenceList('artist');
+
+  t.plan(11);
+
+  t.ok(track(['track:fallen-down', 'Once Upon a Time']));
+  t.ok(artist(['artist:toby-fox', 'Mark Hadley']));
+  t.ok(track(['track:amalgam']));
+  t.ok(track([]));
+
+  let caughtError = null;
+  try {
+    track(['Dog', 'album:vaporwave-2016', 'Cat', 'artist:john-madden']);
+  } catch (err) {
+    caughtError = err;
+  }
+
+  t.not(caughtError, null);
+  t.ok(caughtError instanceof AggregateError);
+  t.equal(caughtError.errors.length, 2);
+  t.ok(caughtError.errors[0] instanceof Error);
+  t.ok(caughtError.errors[0].cause instanceof TypeError);
+  t.ok(caughtError.errors[1] instanceof Error);
+  t.ok(caughtError.errors[0].cause instanceof TypeError);
+});
+
+test(t, 'anyOf', t => {
+  t.plan(11);
+
+  const isStringOrNumber = anyOf(isString, isNumber);
+
+  t.ok(isStringOrNumber('hello world'));
+  t.ok(isStringOrNumber(42));
+  t.throws(() => isStringOrNumber(false));
+
+  const mockError = new Error();
+  const neverSucceeds = () => {
+    throw mockError;
+  };
+
+  const isStringOrGetRekt = anyOf(isString, neverSucceeds);
+
+  t.ok(isStringOrGetRekt('phew!'));
+
+  let caughtError = null;
+  try {
+    isStringOrGetRekt(0xdeadbeef);
+  } catch (err) {
+    caughtError = err;
+  }
+
+  t.not(caughtError, null);
+  t.ok(caughtError instanceof AggregateError);
+  t.equal(caughtError.errors.length, 2);
+  t.ok(caughtError.errors[0] instanceof TypeError);
+  t.equal(caughtError.errors[0].check, isString);
+  t.equal(caughtError.errors[1], mockError);
+  t.equal(caughtError.errors[1].check, neverSucceeds);
+});