parallel mode reporter improvements

- `Suite`s, `Test`s, etc., now have unique identifiers which can optionally be used to re-created object references by a reporter which opts-in to the behavior
- A reporter can swap out the worker’s reporter for a custom one
- fixed an issue in rollup config causing weird problems
- changed how we define `global.Mocha` in `browser-entry.js` (tangential)
- removed `object.assign` polyfill (tangential)
- renamed misnamed `buffered-runner.spec.js` to `parallel-buffered-runner.spec.js`
- added a few unit tests
- refactored some tests; mainly modernizing some syntax

lib/hook.js

@@ -1,7 +1,8 @@
 'use strict';
 
 var Runnable = require('./runnable');
-var inherits = require('./utils').inherits;
+const {inherits, constants} = require('./utils');
+const {MOCHA_ID_PROP_NAME} = constants;
 
 /**
  * Expose `Hook`.
@@ -63,16 +64,21 @@ Hook.prototype.serialize = function serialize() {
   return {
     $$isPending: this.isPending(),
     $$titlePath: this.titlePath(),
-    ctx: {
-      currentTest: {
-        title: this.ctx && this.ctx.currentTest && this.ctx.currentTest.title
-      }
-    },
+    ctx:
+      this.ctx && this.ctx.currentTest
+        ? {
+            currentTest: {
+              title: this.ctx.currentTest.title,
+              [MOCHA_ID_PROP_NAME]: this.ctx.currentTest.id
+            }
+          }
+        : {},
     parent: {
-      root: this.parent.root,
-      title: this.parent.title
+      [MOCHA_ID_PROP_NAME]: this.parent.id
     },
     title: this.title,
-    type: this.type
+    type: this.type,
+    [MOCHA_ID_PROP_NAME]: this.id,
+    __mocha_partial__: true
   };
 };

lib/nodejs/parallel-buffered-runner.js

@@ -12,7 +12,12 @@ const {EVENT_RUN_BEGIN, EVENT_RUN_END} = Runner.constants;
 const debug = require('debug')('mocha:parallel:parallel-buffered-runner');
 const {BufferedWorkerPool} = require('./buffered-worker-pool');
 const {setInterval, clearInterval} = global;
-const {createMap} = require('../utils');
+const {createMap, constants} = require('../utils');
+const {MOCHA_ID_PROP_NAME} = constants;
+
+const DEFAULT_WORKER_REPORTER = require.resolve(
+  './reporters/parallel-buffered'
+);
 
 /**
  * List of options to _not_ serialize for transmission to workers
@@ -68,7 +73,7 @@ const states = createMap({
 /**
  * This `Runner` delegates tests runs to worker threads.  Does not execute any
  * {@link Runnable}s by itself!
- * @private
+ * @public
  */
 class ParallelBufferedRunner extends Runner {
   constructor(...args) {
@@ -88,6 +93,10 @@ class ParallelBufferedRunner extends Runner {
       }
     });
 
+    this._workerReporter = DEFAULT_WORKER_REPORTER;
+    this._linkPartialObjects = false;
+    this._linkedObjectMap = new Map();
+
     this.once(Runner.constants.EVENT_RUN_END, () => {
       this._state = COMPLETE;
     });
@@ -98,12 +107,63 @@ class ParallelBufferedRunner extends Runner {
    * @param {BufferedWorkerPool} pool - Worker pool
    * @param {Options} options - Mocha options
    * @returns {FileRunner} Mapping function
+   * @private
    */
   _createFileRunner(pool, options) {
+    /**
+     * Emits event and sets `BAILING` state, if necessary.
+     * @param {Object} event - Event having `eventName`, maybe `data` and maybe `error`
+     * @param {number} failureCount - Failure count
+     */
+    const emitEvent = (event, failureCount) => {
+      this.emit(event.eventName, event.data, event.error);
+      if (
+        this._state !== BAILING &&
+        event.data &&
+        event.data._bail &&
+        (failureCount || event.error)
+      ) {
+        debug('run(): nonzero failure count & found bail flag');
+        // we need to let the events complete for this file, as the worker
+        // should run any cleanup hooks
+        this._state = BAILING;
+      }
+    };
+
+    /**
+     * Given an event, recursively find any objects in its data that have ID's, and create object references to already-seen objects.
+     * @param {Object} event - Event having `eventName`, maybe `data` and maybe `error`
+     */
+    const linkEvent = event => {
+      const stack = [{parent: event, prop: 'data'}];
+      while (stack.length) {
+        const {parent, prop} = stack.pop();
+        const obj = parent[prop];
+        let newObj;
+        if (obj && typeof obj === 'object' && obj[MOCHA_ID_PROP_NAME]) {
+          const id = obj[MOCHA_ID_PROP_NAME];
+          newObj = this._linkedObjectMap.has(id)
+            ? Object.assign(this._linkedObjectMap.get(id), obj)
+            : obj;
+          this._linkedObjectMap.set(id, newObj);
+          parent[prop] = newObj;
+        } else {
+          newObj = obj;
+        }
+        Object.keys(newObj).forEach(key => {
+          const value = obj[key];
+          if (value && typeof value === 'object' && value[MOCHA_ID_PROP_NAME]) {
+            stack.push({obj: value, parent: newObj, prop: key});
+          }
+        });
+      }
+    };
+
     return async file => {
       debug('run(): enqueueing test file %s', file);
       try {
         const {failureCount, events} = await pool.run(file, options);
+
         if (this._state === BAILED) {
           // short-circuit after a graceful bail. if this happens,
           // some other worker has bailed.
@@ -119,20 +179,18 @@ class ParallelBufferedRunner extends Runner {
         );
         this.failures += failureCount; // can this ever be non-numeric?
         let event = events.shift();
-        while (event) {
-          this.emit(event.eventName, event.data, event.error);
-          if (
-            this._state !== BAILING &&
-            event.data &&
-            event.data._bail &&
-            (failureCount || event.error)
-          ) {
-            debug('run(): nonzero failure count & found bail flag');
-            // we need to let the events complete for this file, as the worker
-            // should run any cleanup hooks
-            this._state = BAILING;
+
+        if (this._linkPartialObjects) {
+          while (event) {
+            linkEvent(event);
+            emitEvent(event, failureCount);
+            event = events.shift();
+          }
+        } else {
+          while (event) {
+            emitEvent(event, failureCount);
+            event = events.shift();
           }
-          event = events.shift();
         }
         if (this._state === BAILING) {
           debug('run(): terminating pool due to "bail" flag');
@@ -166,6 +224,7 @@ class ParallelBufferedRunner extends Runner {
    * Returns the listener for later call to `process.removeListener()`.
    * @param {BufferedWorkerPool} pool - Worker pool
    * @returns {SigIntListener} Listener
+   * @private
    */
   _bindSigIntListener(pool) {
     const sigIntListener = async () => {
@@ -209,15 +268,19 @@ class ParallelBufferedRunner extends Runner {
    * @param {{files: string[], options: Options}} opts - Files to run and
    * command-line options, respectively.
    */
-  run(callback, {files, options} = {}) {
+  run(callback, {files, options = {}} = {}) {
     /**
      * Listener on `Process.SIGINT` which tries to cleanly terminate the worker pool.
      */
     let sigIntListener;
+
+    // assign the reporter the worker will use, which will be different than the
+    // main process' reporter
+    options = {...options, reporter: this._workerReporter};
+
     // This function should _not_ return a `Promise`; its parent (`Runner#run`)
     // returns this instance, so this should do the same. However, we want to make
     // use of `async`/`await`, so we use this IIFE.
-
     (async () => {
       /**
        * This is an interval that outputs stats about the worker pool every so often
@@ -293,6 +356,57 @@ class ParallelBufferedRunner extends Runner {
     })();
     return this;
   }
+
+  /**
+   * Toggle partial object linking behavior; used for building object references from
+   * unique ID's.
+   * @param {boolean} [value] - If `true`, enable partial object linking, otherwise disable
+   * @returns {Runner}
+   * @chainable
+   * @public
+   * @example
+   * // this reporter needs proper object references when run in parallel mode
+   * class MyReporter() {
+   *   constructor(runner) {
+   *     this.runner.linkPartialObjects(true)
+   *       .on(EVENT_SUITE_BEGIN, suite => {
+             // this Suite may be the same object...
+  *       })
+  *       .on(EVENT_TEST_BEGIN, test => {
+  *         // ...as the `test.parent` property
+  *       });
+  *   }
+  * }
+  */
+  linkPartialObjects(value) {
+    this._linkPartialObjects = Boolean(value);
+    return super.linkPartialObjects(value);
+  }
+
+  /**
+   * If this class is the `Runner` in use, then this is going to return `true`.
+   *
+   * For use by reporters.
+   * @returns {true}
+   * @public
+   */
+  isParallelMode() {
+    return true;
+  }
+
+  /**
+   * Configures an alternate reporter for worker processes to use. Subclasses
+   * using worker processes should implement this.
+   * @public
+   * @param {string} path - Absolute path to alternate reporter for worker processes to use
+   * @returns {Runner}
+   * @throws When in serial mode
+   * @chainable
+   */
+  workerReporter(reporter) {
+    this._workerReporter = reporter;
+    return this;
+  }
 }
 
 module.exports = ParallelBufferedRunner;

lib/nodejs/reporters/parallel-buffered.js

@@ -1,7 +1,7 @@
 /**
  * "Buffered" reporter used internally by a worker process when running in parallel mode.
- * @module reporters/parallel-buffered
- * @private
+ * @module nodejs/reporters/parallel-buffered
+ * @public
  */
 
 'use strict';
@@ -53,15 +53,16 @@ const EVENT_NAMES = [
 const ONCE_EVENT_NAMES = [EVENT_DELAY_BEGIN, EVENT_DELAY_END];
 
 /**
- * The `ParallelBuffered` reporter is for use by concurrent runs. Instead of outputting
- * to `STDOUT`, etc., it retains a list of events it receives and hands these
- * off to the callback passed into {@link Mocha#run}. That callback will then
- * return the data to the main process.
- * @private
+ * The `ParallelBuffered` reporter is used by each worker process in "parallel"
+ * mode, by default.  Instead of reporting to to `STDOUT`, etc., it retains a
+ * list of events it receives and hands these off to the callback passed into
+ * {@link Mocha#run}. That callback will then return the data to the main
+ * process.
+ * @public
  */
 class ParallelBuffered extends Base {
   /**
-   * Listens for {@link Runner} events and retains them in an `events` instance prop.
+   * Calls {@link ParallelBuffered#createListeners}
    * @param {Runner} runner
    */
   constructor(runner, opts) {
@@ -70,50 +71,81 @@ class ParallelBuffered extends Base {
     /**
      * Retained list of events emitted from the {@link Runner} instance.
      * @type {BufferedEvent[]}
-     * @memberOf Buffered
+     * @public
      */
-    const events = (this.events = []);
+    this.events = [];
 
     /**
-     * mapping of event names to listener functions we've created,
-     * so we can cleanly _remove_ them from the runner once it's completed.
+     * Map of `Runner` event names to listeners (for later teardown)
+     * @public
+     * @type {Map<string,EventListener>}
      */
-    const listeners = new Map();
+    this.listeners = new Map();
 
-    /**
-     * Creates a listener for event `eventName` and adds it to the `listeners`
-     * map. This is a defensive measure, so that we don't a) leak memory or b)
-     * remove _other_ listeners that may not be associated with this reporter.
-     * @param {string} eventName - Event name
-     */
-    const createListener = eventName =>
-      listeners
-        .set(eventName, (runnable, err) => {
-          events.push(SerializableEvent.create(eventName, runnable, err));
-        })
-        .get(eventName);
+    this.createListeners(runner);
+  }
+
+  /**
+   * Returns a new listener which saves event data in memory to
+   * {@link ParallelBuffered#events}. Listeners are indexed by `eventName` and stored
+   * in {@link ParallelBuffered#listeners}. This is a defensive measure, so that we
+   * don't a) leak memory or b) remove _other_ listeners that may not be
+   * associated with this reporter.
+   *
+   * Subclasses could override this behavior.
+   *
+   * @public
+   * @param {string} eventName - Name of event to create listener for
+   * @returns {EventListener}
+   */
+  createListener(eventName) {
+    const listener = (runnable, err) => {
+      this.events.push(SerializableEvent.create(eventName, runnable, err));
+    };
+    return this.listeners.set(eventName, listener).get(eventName);
+  }
 
+  /**
+   * Creates event listeners (using {@link ParallelBuffered#createListener}) for each
+   * reporter-relevant event emitted by a {@link Runner}. This array is drained when
+   * {@link ParallelBuffered#done} is called by {@link Runner#run}.
+   *
+   * Subclasses could override this behavior.
+   * @public
+   * @param {Runner} runner - Runner instance
+   * @returns {ParallelBuffered}
+   * @chainable
+   */
+  createListeners(runner) {
     EVENT_NAMES.forEach(evt => {
-      runner.on(evt, createListener(evt));
+      runner.on(evt, this.createListener(evt));
     });
     ONCE_EVENT_NAMES.forEach(evt => {
-      runner.once(evt, createListener(evt));
+      runner.once(evt, this.createListener(evt));
     });
 
     runner.once(EVENT_RUN_END, () => {
       debug('received EVENT_RUN_END');
-      listeners.forEach((listener, evt) => {
+      this.listeners.forEach((listener, evt) => {
         runner.removeListener(evt, listener);
-        listeners.delete(evt);
+        this.listeners.delete(evt);
       });
     });
+
+    return this;
   }
 
   /**
    * Calls the {@link Mocha#run} callback (`callback`) with the test failure
    * count and the array of {@link BufferedEvent} objects. Resets the array.
+   *
+   * This is called directly by `Runner#run` and should not be called by any other consumer.
+   *
+   * Subclasses could override this.
+   *
    * @param {number} failures - Number of failed tests
    * @param {Function} callback - The callback passed to {@link Mocha#run}.
+   * @public
    */
   done(failures, callback) {
     callback(SerializableWorkerResult.create(this.events, failures));