data steps: basic custom mocking function support

I checked out a few libraries but none really behaved
the way I needed, and coding it myself means much lower-
level access, which makes certain options a lot easier
(e.g. excluding one argument of a mocked function from
assertion while matching the rest against a pattern).

1 files changed, 262 insertions, 0 deletions

diff --git a/test/lib/generic-mock.js b/test/lib/generic-mock.js
new file mode 100644
index 00000000..841ba462
--- /dev/null
+++ b/test/lib/generic-mock.js
@@ -0,0 +1,262 @@
+import {same} from 'tcompare';
+
+export default function mock(callback) {
+  const mocks = [];
+
+  const track = callback => (...args) => {
+    const {value, close} = callback(...args);
+    mocks.push({close});
+    return value;
+  };
+
+  const mock = {
+    function: track(mockFunction),
+  };
+
+  return {
+    value: callback(mock),
+    close: () => {
+      const errors = [];
+      for (const mock of mocks) {
+        try {
+          mock.close();
+        } catch (error) {
+          errors.push(error);
+        }
+      }
+      if (errors.length) {
+        throw new AggregateError(errors, `Errors closing sub-mocks`);
+      }
+    },
+  };
+}
+
+export function mockFunction(...args) {
+  let name = '(anonymous)';
+  let behavior = null;
+
+  if (args.length === 2) {
+    if (
+      typeof args[0] === 'string' &&
+      typeof args[1] === 'function'
+    ) {
+      name = args[0];
+      behavior = args[1];
+    } else {
+      throw new TypeError(`Expected name to be a string`);
+    }
+  } else if (args.length === 1) {
+    if (typeof args[0] === 'string') {
+      name = args[0];
+    } else if (typeof args[0] === 'function') {
+      behavior = args[0];
+    } else if (args[0] !== null) {
+      throw new TypeError(`Expected string (name), function (behavior), both, or null / no arguments`);
+    }
+  } else if (args.length > 2) {
+    throw new TypeError(`Expected string (name), function (behavior), both, or null / no arguments`);
+  }
+
+  let currentCallDescription = newCallDescription();
+  const allCallDescriptions = [currentCallDescription];
+
+  const topLevelErrors = [];
+  let runningCallCount = 0;
+  let limitCallCount = false;
+  let markedAsOnce = false;
+
+  const fn = (...args) => {
+    const description = processCall(...args);
+    return description.behavior(...args);
+  };
+
+  fn.behavior = value => {
+    if (!(value === null || (
+      typeof value === 'function'
+    ))) {
+      throw new TypeError(`Expected function or null`);
+    }
+
+    currentCallDescription.behavior = behavior;
+    currentCallDescription.described = true;
+
+    return fn;
+  }
+
+  fn.argumentCount = value => {
+    if (!(value === null || (
+      typeof value === 'number' &&
+      value === parseInt(value) &&
+      value >= 0
+    ))) {
+      throw new TypeError(`Expected whole number or null`);
+    }
+
+    if (currentCallDescription.argsPattern) {
+      throw new TypeError(`Unexpected .argumentCount() when .args() has been called`);
+    }
+
+    currentCallDescription.argsPattern = {length: value};
+    currentCallDescription.described = true;
+
+    return fn;
+  };
+
+  fn.args = (...args) => {
+    const value = args[0];
+
+    if (args.length > 1 || !(value === null || Array.isArray(value))) {
+      throw new TypeError(`Expected one array or null`);
+    }
+
+    currentCallDescription.argsPattern = Object.fromEntries(
+      value
+        .map((v, i) => v === undefined ? false : [i, v])
+        .filter(Boolean)
+        .concat([['length', value.length]]));
+
+    currentCallDescription.described = true;
+
+    return fn;
+  };
+
+  fn.once = (...args) => {
+    if (args.length) {
+      throw new TypeError(`Didn't expect any arguments`);
+    }
+
+    if (allCallDescriptions.length > 1) {
+      throw new TypeError(`Unexpected .once() when providing multiple descriptions`);
+    }
+
+    limitCallCount = true;
+    markedAsOnce = true;
+
+    return fn;
+  };
+
+  fn.next = (...args) => {
+    if (args.length) {
+      throw new TypeError(`Didn't expect any arguments`);
+    }
+
+    if (markedAsOnce) {
+      throw new TypeError(`Unexpected .next() when .once() has been called`);
+    }
+
+    currentCallDescription = newCallDescription();
+    allCallDescriptions.push(currentCallDescription);
+
+    limitCallCount = true;
+    return fn;
+  };
+
+  fn.repeat = times => {
+    // Note: This function should be called AFTER filling out the
+    // call description which is being repeated.
+
+    if (!(
+      typeof value === 'number' &&
+      value === parseInt(value) &&
+      value >= 2
+    )) {
+      throw new TypeError(`Expected whole number of at least 2`);
+    }
+
+    if (markedAsOnce) {
+      throw new TypeError(`Unexpected .repeat() when .once() has been called`);
+    }
+
+    // The current call description is already in the full list,
+    // so skip the first push.
+    for (let i = 2; i <= times; i++) {
+      allCallDescriptions.push(currentCallDescription);
+    }
+
+    // Prep a new description like when calling .next().
+    currentCallDescription = newCallDescription();
+    allCallDescriptions.push(currentCallDescription);
+
+    limitCallCount = true;
+
+    return fn;
+  };
+
+  return {
+    value: fn,
+    close: () => {
+      if (topLevelErrors.length) {
+        throw new AggregateError(topLevelErrors, `Errors in mock ${name}`);
+      }
+    },
+  };
+
+  function newCallDescription() {
+    return {
+      described: false,
+      behavior: behavior ?? null,
+      argumentCount: null,
+      argsPattern: null,
+    };
+  }
+
+  function processCall(...args) {
+    const callErrors = [];
+
+    runningCallCount++;
+    const currentCallNumber = runningCallCount;
+    const currentDescription = selectCallDescription(currentCallNumber);
+
+    const {
+      argumentCount,
+      argsPattern,
+    } = currentDescription;
+
+    if (argumentCount !== null) {
+      if (args.length !== argumentCount) {
+        callErrors.push(new Error(`Argument count mismatch: expected ${argumentCount}, got ${args.length}`));
+      }
+    }
+
+    if (argsPattern !== null) {
+      const keysToCheck = Object.keys(argsPattern);
+      const argsAsObject = Object.fromEntries(
+        args
+          .map((v, i) => [i.toString(), v])
+          .filter(([i]) => keysToCheck.includes(i))
+          .concat([['length', args.length]]));
+
+      const {match, diff} = same(argsAsObject, argsPattern);
+      if (!match) {
+        callErrors.push(new Error(`Argument pattern mismatch:\n` + diff));
+      }
+    }
+
+    if (callErrors.length) {
+      const aggregate = new AggregateError(callErrors, `Errors in call #${currentCallNumber}`);
+      topLevelErrors.push(aggregate);
+    }
+
+    return currentDescription;
+  }
+
+  function selectCallDescription(currentCallNumber) {
+    // console.log(currentCallNumber, allCallDescriptions[0]);
+
+    const lastDescription = allCallDescriptions[allCallDescriptions.length - 1];
+    const describedCount =
+      (lastDescription.described
+        ? allCallDescriptions.length
+        : allCallDescriptions.length - 1);
+
+    if (currentCallNumber > describedCount) {
+      if (lastDescription.described) {
+        return newCallDescription();
+      } else {
+        return lastDescription;
+      }
+    } else {
+      return allCallDescriptions[currentCallNumber - 1];
+    }
+  }
+}