feat: add new 'modern' implementation of Fake Timers

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Features
 
 - `[jest-environment-jsdom]` [**BREAKING**] Upgrade `jsdom` to v16 ([#9606](https://github.com/facebook/jest/pull/9606))
+- `[@jest/fake-timers]` Add possibility to use a modern implementation of fake timers, backed by `@sinonjs/fake-timers` ([#7776](https://github.com/facebook/jest/pull/7776))
 
 ### Fixes
 

docs/Configuration.md

@@ -1124,7 +1124,9 @@ This option sets the URL for the jsdom environment. It is reflected in propertie
 
 Default: `real`
 
-Setting this value to `fake` allows the use of fake timers for functions such as `setTimeout`. Fake timers are useful when a piece of code sets a long timeout that we don't want to wait for in a test.
+Setting this value to `legacy` or `fake` allows the use of fake timers for functions such as `setTimeout`. Fake timers are useful when a piece of code sets a long timeout that we don't want to wait for in a test.
+
+If the value is `modern`, [`@sinonjs/fake-timers`](https://github.com/sinonjs/fake-timers) will be used as implementation instead of Jest's own legacy implementation. This will be the default fake implementation in Jest 27.
 
 ### `transform` [object\<string, pathToTransformer | [pathToTransformer, object]>]
 

docs/JestObjectAPI.md

@@ -577,10 +577,12 @@ Restores all mocks back to their original value. Equivalent to calling [`.mockRe
 
 ## Mock timers
 
-### `jest.useFakeTimers()`
+### `jest.useFakeTimers(implementation?: 'modern' | 'legacy')`
 
 Instructs Jest to use fake versions of the standard timer functions (`setTimeout`, `setInterval`, `clearTimeout`, `clearInterval`, `nextTick`, `setImmediate` and `clearImmediate`).
 
+If you pass `'modern'` as argument, [`@sinonjs/fake-timers`](https://github.com/sinonjs/fake-timers) will be used as implementation instead of Jest's own fake timers. This also mocks additional timers like `Date`. `'modern'` will be the default behavior in Jest 27.
+
 Returns the `jest` object for chaining.
 
 ### `jest.useRealTimers()`
@@ -607,6 +609,8 @@ This is often useful for synchronously executing setTimeouts during a test in or
 
 Exhausts all tasks queued by `setImmediate()`.
 
+> Note: This function is not available when using modern fake timers implementation
+
 ### `jest.advanceTimersByTime(msToRun)`
 
 ##### renamed in Jest **22.0.0+**
@@ -639,6 +643,18 @@ This means, if any timers have been scheduled (but have not yet executed), they
 
 Returns the number of fake timers still left to run.
 
+### `.jest.setSystemTime()`
+
+Set the current system time used by fake timers. Simulates a user changing the system clock while your program is running. It affects the current time but it does not in itself cause e.g. timers to fire; they will fire exactly as they would have done without the call to `jest.setSystemTime()`.
+
+> Note: This function is only available when using modern fake timers implementation
+
+### `.jest.getRealSystemTime()`
+
+When mocking time, `Date.now()` will also be mocked. If you for some reason need access to the real current time, you can invoke this function.
+
+> Note: This function is only available when using modern fake timers implementation
+
 ## Misc
 
 ### `jest.setTimeout(timeout)`

e2e/__tests__/modernFakeTimers.test.ts

@@ -0,0 +1,20 @@
+/**
+ * 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 runJest from '../runJest';
+
+describe('modern implementation of fake timers', () => {
+  it('should be possible to use modern implementation from config', () => {
+    const result = runJest('modern-fake-timers/from-config');
+    expect(result.exitCode).toBe(0);
+  });
+
+  it('should be possible to use modern implementation from jest-object', () => {
+    const result = runJest('modern-fake-timers/from-jest-object');
+    expect(result.exitCode).toBe(0);
+  });
+});

e2e/modern-fake-timers/from-config/__tests__/test.js

@@ -0,0 +1,18 @@
+/**
+ * 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.
+ */
+
+'use strict';
+
+test('fake timers', () => {
+  jest.setSystemTime(0);
+
+  expect(Date.now()).toBe(0);
+
+  jest.setSystemTime(1000);
+
+  expect(Date.now()).toBe(1000);
+});

e2e/modern-fake-timers/from-config/package.json

@@ -0,0 +1,6 @@
+{
+  "jest": {
+    "timers": "modern",
+    "testEnvironment": "node"
+  }
+}

e2e/modern-fake-timers/from-jest-object/__tests__/test.js

@@ -0,0 +1,20 @@
+/**
+ * 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.
+ */
+
+'use strict';
+
+test('fake timers', () => {
+  jest.useFakeTimers('modern');
+
+  jest.setSystemTime(0);
+
+  expect(Date.now()).toBe(0);
+
+  jest.setSystemTime(1000);
+
+  expect(Date.now()).toBe(1000);
+});

e2e/modern-fake-timers/from-jest-object/package.json

@@ -0,0 +1,5 @@
+{
+  "jest": {
+    "testEnvironment": "node"
+  }
+}

packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapter.ts

@@ -49,9 +49,11 @@ const jestAdapter = async (
     testPath,
   });
 
-  if (config.timers === 'fake') {
+  if (config.timers === 'fake' || config.timers === 'legacy') {
     // during setup, this cannot be null (and it's fine to explode if it is)
     environment.fakeTimers!.useFakeTimers();
+  } else if (config.timers === 'modern') {
+    environment.fakeTimersModern!.useFakeTimers();
   }
 
   globals.beforeEach(() => {

packages/jest-environment/src/index.ts

@@ -199,6 +199,8 @@ export interface Jest {
   retryTimes(numRetries: number): Jest;
   /**
    * Exhausts tasks queued by setImmediate().
+   *
+   * > Note: This function is not available when using Lolex as fake timers implementation
    */
   runAllImmediates(): void;
   /**
@@ -269,7 +271,7 @@ export interface Jest {
   /**
    * Instructs Jest to use fake versions of the standard timer functions.
    */
-  useFakeTimers(): Jest;
+  useFakeTimers(implementation?: 'modern' | 'legacy'): Jest;
   /**
    * Instructs Jest to use the real versions of the standard timer functions.
    */
@@ -281,4 +283,18 @@ export interface Jest {
    * every test so that local module state doesn't conflict between tests.
    */
   isolateModules(fn: () => void): Jest;
+
+  /**
+   * When mocking time, `Date.now()` will also be mocked. If you for some reason need access to the real current time, you can invoke this function.
+   *
+   * > Note: This function is only available when using Lolex as fake timers implementation
+   */
+  getRealSystemTime(): number;
+
+  /**
+   *  Set the current system time used by fake timers. Simulates a user changing the system clock while your program is running. It affects the current time but it does not in itself cause e.g. timers to fire; they will fire exactly as they would have done without the call to `jest.setSystemTime()`.
+   *
+   *  > Note: This function is only available when using Lolex as fake timers implementation
+   */
+  setSystemTime(now?: number): void;
 }

packages/jest-jasmine2/src/index.ts

@@ -93,8 +93,10 @@ async function jasmine2(
   environment.global.describe.skip = environment.global.xdescribe;
   environment.global.describe.only = environment.global.fdescribe;
 
-  if (config.timers === 'fake') {
+  if (config.timers === 'fake' || config.timers === 'legacy') {
     environment.fakeTimers!.useFakeTimers();
+  } else if (config.timers === 'modern') {
+    environment.fakeTimersModern!.useFakeTimers();
   }
 
   env.beforeEach(() => {
@@ -109,7 +111,7 @@ async function jasmine2(
     if (config.resetMocks) {
       runtime.resetAllMocks();
 
-      if (config.timers === 'fake') {
+      if (config.timers === 'fake' || config.timers === 'legacy') {
         environment.fakeTimers!.useFakeTimers();
       }
     }

packages/jest-runtime/package.json

@@ -13,6 +13,7 @@
     "@jest/console": "^26.0.0-alpha.0",
     "@jest/environment": "^26.0.0-alpha.0",
     "@jest/globals": "^26.0.0-alpha.0",
+    "@jest/fake-timers": "^26.0.0-alpha.0",
     "@jest/source-map": "^26.0.0-alpha.0",
     "@jest/test-result": "^26.0.0-alpha.0",
     "@jest/transform": "^26.0.0-alpha.0",

packages/jest-runtime/src/index.ts

@@ -28,6 +28,7 @@ import type {
 } from '@jest/environment';
 import type * as JestGlobals from '@jest/globals';
 import type {SourceMapRegistry} from '@jest/source-map';
+import {LegacyFakeTimers, ModernFakeTimers} from '@jest/fake-timers';
 import {formatStackTrace, separateMessageFromStack} from 'jest-message-util';
 import {createDirectory, deepCyclicCopy} from 'jest-util';
 import {escapePathForRegex} from 'jest-regex-util';
@@ -134,6 +135,10 @@ class Runtime {
   private _currentlyExecutingModulePath: string;
   private _environment: JestEnvironment;
   private _explicitShouldMock: BooleanMap;
+  private _fakeTimersImplementation:
+    | LegacyFakeTimers<unknown>
+    | ModernFakeTimers
+    | null;
   private _internalModuleRegistry: ModuleRegistry;
   private _isCurrentlyExecutingManualMock: string | null;
   private _mockFactories: Map<string, () => unknown>;
@@ -205,6 +210,11 @@ class Runtime {
     this._shouldUnmockTransitiveDependenciesCache = new Map();
     this._transitiveShouldMock = new Map();
 
+    this._fakeTimersImplementation =
+      config.timers === 'modern'
+        ? this._environment.fakeTimersModern
+        : this._environment.fakeTimers;
+
     this._unmockList = unmockRegExpCache.get(config);
     if (!this._unmockList && config.unmockedModulePathPatterns) {
       this._unmockList = new RegExp(
@@ -1410,8 +1420,25 @@ class Runtime {
       this.restoreAllMocks();
       return jestObject;
     };
-    const useFakeTimers = () => {
-      _getFakeTimers().useFakeTimers();
+    const _getFakeTimers = () => {
+      if (
+        !(this._environment.fakeTimers || this._environment.fakeTimersModern)
+      ) {
+        this._logFormattedReferenceError(
+          'You are trying to access a property or method of the Jest environment after it has been torn down.',
+        );
+        process.exitCode = 1;
+      }
+
+      return this._fakeTimersImplementation!;
+    };
+    const useFakeTimers = (type: string = 'legacy') => {
+      if (type === 'modern') {
+        this._fakeTimersImplementation = this._environment.fakeTimersModern;
+      } else {
+        this._fakeTimersImplementation = this._environment.fakeTimers;
+      }
+      this._fakeTimersImplementation!.useFakeTimers();
       return jestObject;
     };
     const useRealTimers = () => {
@@ -1445,18 +1472,6 @@ class Runtime {
       return jestObject;
     };
 
-    const _getFakeTimers = (): NonNullable<JestEnvironment['fakeTimers']> => {
-      if (!this._environment.fakeTimers) {
-        this._logFormattedReferenceError(
-          'You are trying to access a property or method of the Jest environment after it has been torn down.',
-        );
-        process.exitCode = 1;
-      }
-
-      // We've logged a user message above, so it doesn't matter if we return `null` here
-      return this._environment.fakeTimers!;
-    };
-
     const jestObject: Jest = {
       addMatchers: (matchers: Record<string, any>) =>
         this._environment.global.jasmine.addMatchers(matchers),
@@ -1476,6 +1491,17 @@ class Runtime {
       fn,
       genMockFromModule: (moduleName: string) =>
         this._generateMock(from, moduleName),
+      getRealSystemTime: () => {
+        const fakeTimers = _getFakeTimers();
+
+        if (fakeTimers instanceof ModernFakeTimers) {
+          return fakeTimers.getRealSystemTime();
+        } else {
+          throw new TypeError(
+            'getRealSystemTime is not available when not using modern timers',
+          );
+        }
+      },
       getTimerCount: () => _getFakeTimers().getTimerCount(),
       isMockFunction: this._moduleMocker.isMockFunction,
       isolateModules,
@@ -1487,14 +1513,35 @@ class Runtime {
       resetModules,
       restoreAllMocks,
       retryTimes,
-      runAllImmediates: () => _getFakeTimers().runAllImmediates(),
+      runAllImmediates: () => {
+        const fakeTimers = _getFakeTimers();
+
+        if (fakeTimers instanceof LegacyFakeTimers) {
+          fakeTimers.runAllImmediates();
+        } else {
+          throw new TypeError(
+            'runAllImmediates is not available when using modern timers',
+          );
+        }
+      },
       runAllTicks: () => _getFakeTimers().runAllTicks(),
       runAllTimers: () => _getFakeTimers().runAllTimers(),
       runOnlyPendingTimers: () => _getFakeTimers().runOnlyPendingTimers(),
       runTimersToTime: (msToRun: number) =>
         _getFakeTimers().advanceTimersByTime(msToRun),
       setMock: (moduleName: string, mock: unknown) =>
         setMockFactory(moduleName, () => mock),
+      setSystemTime: (now?: number) => {
+        const fakeTimers = _getFakeTimers();
+
+        if (fakeTimers instanceof ModernFakeTimers) {
+          fakeTimers.setSystemTime(now);
+        } else {
+          throw new TypeError(
+            'setSystemTime is not available when not using modern timers',
+          );
+        }
+      },
       setTimeout,
       spyOn,
       unmock,

packages/jest-runtime/tsconfig.json

@@ -9,6 +9,7 @@
     {"path": "../jest-console"},
     {"path": "../jest-environment"},
     {"path": "../jest-environment-node"},
+    {"path": "../jest-fake-timers"},
     {"path": "../jest-globals"},
     {"path": "../jest-haste-map"},
     {"path": "../jest-message-util"},

packages/jest-types/src/Config.ts

@@ -344,7 +344,7 @@ export type ProjectConfig = {
   testRegex: Array<string | RegExp>;
   testRunner: string;
   testURL: string;
-  timers: 'real' | 'fake';
+  timers: 'real' | 'fake' | 'modern' | 'legacy';
   transform: Array<[string, Path, Record<string, unknown>]>;
   transformIgnorePatterns: Array<Glob>;
   watchPathIgnorePatterns: Array<string>;