feat: add fake timers implementation backed by Lolex (#8897)

CHANGELOG.md

@@ -8,6 +8,7 @@
 - `[jest-diff]` [**BREAKING**] Export as ECMAScript module ([#8873](https://github.com/facebook/jest/pull/8873))
 - `[jest-diff]` Add `includeChangeCounts` and rename `Indicator` options ([#8881](https://github.com/facebook/jest/pull/8881))
 - `[jest-diff]` Add `changeColor` and `patchColor` options ([#8911](https://github.com/facebook/jest/pull/8911))
+- `[@jest/fake-timers]` Add Lolex as implementation of fake timers ([#8897](https://github.com/facebook/jest/pull/8897))
 - `[jest-runner]` Warn if a worker had to be force exited ([#8206](https://github.com/facebook/jest/pull/8206))
 - `[@jest/test-result]` Create method to create empty `TestResult` ([#8867](https://github.com/facebook/jest/pull/8867))
 - `[jest-worker]` [**BREAKING**] Return a promise from `end()`, resolving with the information whether workers exited gracefully ([#8206](https://github.com/facebook/jest/pull/8206))

e2e/timer-reset-mocks/after-reset-all-mocks/timerAndMock.test.js

@@ -9,17 +9,17 @@ describe('timers', () => {
   it('should work before calling resetAllMocks', () => {
     jest.useFakeTimers();
     const f = jest.fn();
-    setImmediate(() => f());
-    jest.runAllImmediates();
-    expect(f.mock.calls.length).toBe(1);
+    setTimeout(f, 0);
+    jest.runAllTimers();
+    expect(f).toHaveBeenCalledTimes(1);
   });
 
   it('should not break after calling resetAllMocks', () => {
     jest.resetAllMocks();
     jest.useFakeTimers();
     const f = jest.fn();
-    setImmediate(() => f());
-    jest.runAllImmediates();
-    expect(f.mock.calls.length).toBe(1);
+    setTimeout(f, 0);
+    jest.runAllTimers();
+    expect(f).toHaveBeenCalledTimes(1);
   });
 });

e2e/timer-reset-mocks/with-reset-mocks/timerWithMock.test.js

@@ -9,8 +9,8 @@ describe('timers', () => {
   it('should work before calling resetAllMocks', () => {
     const f = jest.fn();
     jest.useFakeTimers();
-    setImmediate(() => f());
-    jest.runAllImmediates();
-    expect(f.mock.calls.length).toBe(1);
+    setTimeout(f, 0);
+    jest.runAllTimers();
+    expect(f).toHaveBeenCalledTimes(1);
   });
 });

examples/timer/__tests__/infinite_timer_game.test.js

@@ -5,15 +5,16 @@
 jest.useFakeTimers();
 
 it('schedules a 10-second timer after 1 second', () => {
+  jest.spyOn(global, 'setTimeout');
   const infiniteTimerGame = require('../infiniteTimerGame');
   const callback = jest.fn();
 
   infiniteTimerGame(callback);
 
   // At this point in time, there should have been a single call to
   // setTimeout to schedule the end of the game in 1 second.
-  expect(setTimeout.mock.calls.length).toBe(1);
-  expect(setTimeout.mock.calls[0][1]).toBe(1000);
+  expect(setTimeout).toBeCalledTimes(1);
+  expect(setTimeout).toHaveBeenNthCalledWith(1, expect.any(Function), 1000);
 
   // Fast forward and exhaust only currently pending timers
   // (but not any new timers that get created during that process)
@@ -24,6 +25,6 @@ it('schedules a 10-second timer after 1 second', () => {
 
   // And it should have created a new timer to start the game over in
   // 10 seconds
-  expect(setTimeout.mock.calls.length).toBe(2);
-  expect(setTimeout.mock.calls[1][1]).toBe(10000);
+  expect(setTimeout).toBeCalledTimes(2);
+  expect(setTimeout).toHaveBeenNthCalledWith(2, expect.any(Function), 10000);
 });

examples/timer/__tests__/timer_game.test.js

@@ -5,12 +5,15 @@
 jest.useFakeTimers();
 
 describe('timerGame', () => {
+  beforeEach(() => {
+    jest.spyOn(global, 'setTimeout');
+  });
   it('waits 1 second before ending the game', () => {
     const timerGame = require('../timerGame');
     timerGame();
 
-    expect(setTimeout.mock.calls.length).toBe(1);
-    expect(setTimeout.mock.calls[0][1]).toBe(1000);
+    expect(setTimeout).toBeCalledTimes(1);
+    expect(setTimeout).toBeCalledWith(expect.any(Function), 1000);
   });
 
   it('calls the callback after 1 second via runAllTimers', () => {
@@ -27,7 +30,7 @@ describe('timerGame', () => {
 
     // Now our callback should have been called!
     expect(callback).toBeCalled();
-    expect(callback.mock.calls.length).toBe(1);
+    expect(callback).toBeCalledTimes(1);
   });
 
   it('calls the callback after 1 second via advanceTimersByTime', () => {
@@ -44,6 +47,6 @@ describe('timerGame', () => {
 
     // Now our callback should have been called!
     expect(callback).toBeCalled();
-    expect(callback.mock.calls.length).toBe(1);
+    expect(callback).toBeCalledTimes(1);
   });
 });

packages/jest-fake-timers/package.json

@@ -13,7 +13,11 @@
     "@jest/types": "^24.9.0",
     "jest-message-util": "^24.9.0",
     "jest-mock": "^24.9.0",
-    "jest-util": "^24.9.0"
+    "jest-util": "^24.9.0",
+    "lolex": "^4.2.0"
+  },
+  "devDependencies": {
+    "@types/lolex": "^3.1.1"
   },
   "engines": {
     "node": ">= 8"

packages/jest-fake-timers/src/FakeTimersLolex.ts

@@ -0,0 +1,154 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  InstalledClock,
+  LolexWithContext,
+  withGlobal as lolexWithGlobal,
+} from 'lolex';
+import {StackTraceConfig, formatStackTrace} from 'jest-message-util';
+
+export default class FakeTimers {
+  private _clock!: InstalledClock;
+  private _config: StackTraceConfig;
+  private _fakingTime: boolean;
+  private _global: NodeJS.Global;
+  private _lolex: LolexWithContext;
+  private _maxLoops: number;
+
+  constructor({
+    global,
+    config,
+    maxLoops,
+  }: {
+    global: NodeJS.Global;
+    config: StackTraceConfig;
+    maxLoops?: number;
+  }) {
+    this._global = global;
+    this._config = config;
+    this._maxLoops = maxLoops || 100000;
+
+    this._fakingTime = false;
+    this._lolex = lolexWithGlobal(global);
+  }
+
+  clearAllTimers() {
+    if (this._fakingTime) {
+      this._clock.reset();
+    }
+  }
+
+  dispose() {
+    this.useRealTimers();
+  }
+
+  runAllTimers() {
+    if (this._checkFakeTimers()) {
+      this._clock.runAll();
+    }
+  }
+
+  runOnlyPendingTimers() {
+    if (this._checkFakeTimers()) {
+      this._clock.runToLast();
+    }
+  }
+
+  advanceTimersToNextTimer(steps = 1) {
+    if (this._checkFakeTimers()) {
+      for (let i = steps; i > 0; i--) {
+        this._clock.next();
+        // Fire all timers at this point: https://github.com/sinonjs/lolex/issues/250
+        this._clock.tick(0);
+
+        if (this._clock.countTimers() === 0) {
+          break;
+        }
+      }
+    }
+  }
+
+  advanceTimersByTime(msToRun: number) {
+    if (this._checkFakeTimers()) {
+      this._clock.tick(msToRun);
+    }
+  }
+
+  runAllTicks() {
+    if (this._checkFakeTimers()) {
+      // @ts-ignore
+      this._clock.runMicrotasks();
+    }
+  }
+
+  useRealTimers() {
+    if (this._fakingTime) {
+      this._clock.uninstall();
+      this._fakingTime = false;
+    }
+  }
+
+  useFakeTimers() {
+    const toFake = Object.keys(this._lolex.timers) as Array<
+      keyof LolexWithContext['timers']
+    >;
+
+    if (!this._fakingTime) {
+      this._clock = this._lolex.install({
+        loopLimit: this._maxLoops,
+        now: Date.now(),
+        target: this._global,
+        toFake,
+      });
+
+      this._fakingTime = true;
+    }
+  }
+
+  reset() {
+    if (this._checkFakeTimers()) {
+      const {now} = this._clock;
+      this._clock.reset();
+      this._clock.setSystemTime(now);
+    }
+  }
+
+  setSystemTime(now?: number) {
+    if (this._checkFakeTimers()) {
+      this._clock.setSystemTime(now);
+    }
+  }
+
+  getRealSystemTime() {
+    return Date.now();
+  }
+
+  getTimerCount() {
+    if (this._checkFakeTimers()) {
+      return this._clock.countTimers();
+    }
+
+    return 0;
+  }
+
+  private _checkFakeTimers() {
+    if (!this._fakingTime) {
+      this._global.console.warn(
+        'A function to advance timers was called but the timers API is not ' +
+          'mocked with fake timers. Call `jest.useFakeTimers()` in this test or ' +
+          'enable fake timers globally by setting `"timers": "fake"` in the ' +
+          'configuration file\nStack Trace:\n' +
+          formatStackTrace(new Error().stack!, this._config, {
+            noStackTrace: false,
+          }),
+      );
+    }
+
+    return this._fakingTime;
+  }
+}

packages/jest-fake-timers/src/__tests__/__snapshots__/fakeTimersLolex.test.ts.snap

@@ -0,0 +1,3 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`FakeTimers runAllTimers warns when trying to advance timers while real timers are used 1`] = `"A function to advance timers was called but the timers API is not mocked with fake timers. Call \`jest.useFakeTimers()\` in this test or enable fake timers globally by setting \`\\"timers\\": \\"fake\\"\` in the configuration file"`;