feat(fake-timers)!: allow jest.useFakeTimers() and `projectConfig.f…

…akeTimers` to take an options bag (#12572)

CHANGELOG.md

@@ -7,6 +7,7 @@
 - `[jest-circus, jest-jasmine2]` Allowed classes and functions as `describe` and `it`/`test` names ([#12484](https://github.com/facebook/jest/pull/12484))
 - `[jest-cli, jest-config]` [**BREAKING**] Remove `testURL` config, use `testEnvironmentOptions.url` instead ([#10797](https://github.com/facebook/jest/pull/10797))
 - `[jest-cli, jest-core]` Add `--shard` parameter for distributed parallel test execution ([#12546](https://github.com/facebook/jest/pull/12546))
+- `[jest-cli]` [**BREAKING**] Remove undocumented `--timers` option ([#12572](https://github.com/facebook/jest/pull/12572))
 - `[jest-config]` [**BREAKING**] Stop shipping `jest-environment-jsdom` by default ([#12354](https://github.com/facebook/jest/pull/12354))
 - `[jest-config]` [**BREAKING**] Stop shipping `jest-jasmine2` by default ([#12355](https://github.com/facebook/jest/pull/12355))
 - `[jest-config, @jest/types]` Add `ci` to `GlobalConfig` ([#12378](https://github.com/facebook/jest/pull/12378))
@@ -24,6 +25,8 @@
 - `[jest-environment-node]` [**BREAKING**] Second argument `context` to constructor is mandatory ([#12469](https://github.com/facebook/jest/pull/12469))
 - `[@jest/expect]` New module which extends `expect` with `jest-snapshot` matchers ([#12404](https://github.com/facebook/jest/pull/12404), [#12410](https://github.com/facebook/jest/pull/12410), [#12418](https://github.com/facebook/jest/pull/12418))
 - `[@jest/expect-utils]` New module exporting utils for `expect` ([#12323](https://github.com/facebook/jest/pull/12323))
+- `[@jest/fake-timers]` [**BREAKING**] Rename `timers` configuration option to `fakeTimers` ([#12572](https://github.com/facebook/jest/pull/12572))
+- `[@jest/fake-timers]` [**BREAKING**] Allow `jest.useFakeTimers()` and `projectConfig.fakeTimers` to take an options bag ([#12572](https://github.com/facebook/jest/pull/12572))
 - `[jest-haste-map]` [**BREAKING**] `HasteMap.create` now returns a promise ([#12008](https://github.com/facebook/jest/pull/12008))
 - `[jest-haste-map]` Add support for `dependencyExtractor` written in ESM ([#12008](https://github.com/facebook/jest/pull/12008))
 - `[jest-mock]` [**BREAKING**] Rename exported utility types `ClassLike`, `FunctionLike`, `ConstructorLikeKeys`, `MethodLikeKeys`, `PropertyLikeKeys`; remove exports of utility types `ArgumentsOf`, `ArgsType`, `ConstructorArgumentsOf` - TS builtin utility types `ConstructorParameters` and `Parameters` should be used instead ([#12435](https://github.com/facebook/jest/pull/12435), [#12489](https://github.com/facebook/jest/pull/12489))

docs/Configuration.md

@@ -395,6 +395,108 @@ Jest's ESM support is still experimental, see [its docs for more details](ECMASc
 }
 ```
 
+### `fakeTimers` \[object]
+
+Default: `{}`
+
+The fake timers may be useful when a piece of code sets a long timeout that we don't want to wait for in a test. For additional details see [Fake Timers guide](TimerMocks.md) and [API documentation](JestObjectAPI.md#fake-timers).
+
+This option provides the default configuration of fake timers for all tests. Calling `jest.useFakeTimers()` in a test file will use these options or will override them if a configuration object is passed. For example, you can tell Jest to keep the original implementation of `process.nextTick()` and adjust the limit of recursive timers that will be run:
+
+```json
+{
+  "fakeTimers": {
+    "doNotFake": ["nextTick"],
+    "timerLimit": 1000
+  }
+}
+```
+
+```js title="fakeTime.test.js"
+// install fake timers for this file using the options from Jest configuration
+jest.useFakeTimers();
+
+test('increase the limit of recursive timers for this and following tests', () => {
+  jest.useFakeTimers({timerLimit: 5000});
+  // ...
+});
+```
+
+:::tip
+
+Instead of including `jest.useFakeTimers()` in each test file, you can enable fake timers globally for all tests:
+
+```json
+{
+  "fakeTimers": {
+    "enableGlobally": true
+  }
+}
+```
+
+:::
+
+Configuration options:
+
+```ts
+type FakeableAPI =
+  | 'Date'
+  | 'hrtime'
+  | 'nextTick'
+  | 'performance'
+  | 'queueMicrotask'
+  | 'requestAnimationFrame'
+  | 'cancelAnimationFrame'
+  | 'requestIdleCallback'
+  | 'cancelIdleCallback'
+  | 'setImmediate'
+  | 'clearImmediate'
+  | 'setInterval'
+  | 'clearInterval'
+  | 'setTimeout'
+  | 'clearTimeout';
+
+type ModernFakeTimersConfig = {
+  /**
+   * If set to `true` all timers will be advanced automatically by 20 milliseconds
+   * every 20 milliseconds. A custom time delta may be provided by passing a number.
+   * The default is `false`.
+   */
+  advanceTimers?: boolean | number;
+  /**
+   * List of names of APIs that should not be faked. The default is `[]`, meaning
+   * all APIs are faked.
+   */
+  doNotFake?: Array<FakeableAPI>;
+  /** Whether fake timers should be enabled for all test files. The default is `false`. */
+  enableGlobally?: boolean;
+  /**
+   * Use the old fake timers implementation instead of one backed by `@sinonjs/fake-timers`.
+   * The default is `false`.
+   */
+  legacyFakeTimers?: boolean;
+  /** Sets current system time to be used by fake timers. The default is `Date.now()`. */
+  now?: number;
+  /** Maximum number of recursive timers that will be run. The default is `100_000` timers. */
+  timerLimit?: number;
+};
+```
+
+:::info Legacy Fake Timers
+
+For some reason you might have to use legacy implementation of fake timers. Here is how to enable it globally (additional options are not supported):
+
+```json
+{
+  "fakeTimers": {
+    "enableGlobally": true,
+    "legacyFakeTimers": true
+  }
+}
+```
+
+:::
+
 ### `forceCoverageMatch` \[array&lt;string&gt;]
 
 Default: `['']`
@@ -1458,14 +1560,6 @@ Default: `5000`
 
 Default timeout of a test in milliseconds.
 
-### `timers` \[string]
-
-Default: `real`
-
-Setting this value to `fake` or `modern` enables fake timers for all tests by default. Fake timers are useful when a piece of code sets a long timeout that we don't want to wait for in a test. You can learn more about fake timers [here](JestObjectAPI.md#jestusefaketimersimplementation-modern--legacy).
-
-If the value is `legacy`, the old implementation will be used as implementation instead of one backed by [`@sinonjs/fake-timers`](https://github.com/sinonjs/fake-timers).
-
 ### `transform` \[object&lt;string, pathToTransformer | \[pathToTransformer, object]&gt;]
 
 Default: `{"\\.[jt]sx?$": "babel-jest"}`

docs/JestObjectAPI.md

@@ -628,19 +628,118 @@ test('direct', () => {
 });
 ```
 
-## Mock Timers
+## Fake Timers
 
-### `jest.useFakeTimers(implementation?: 'modern' | 'legacy')`
+### `jest.useFakeTimers(fakeTimersConfig?)`
 
-Instructs Jest to use fake versions of the standard timer functions (`setTimeout`, `setInterval`, `clearTimeout`, `clearInterval`, `nextTick`, `setImmediate` and `clearImmediate` as well as `Date`).
+Instructs Jest to use fake versions of the global date, performance, time and timer APIs. Fake timers implementation is backed by [`@sinonjs/fake-timers`](https://github.com/sinonjs/fake-timers).
 
-If you pass `'legacy'` as an argument, Jest's legacy implementation will be used rather than one based on [`@sinonjs/fake-timers`](https://github.com/sinonjs/fake-timers).
+Fake timers will swap out `Date`, `performance.now()`, `queueMicrotask()`, `setImmediate()`, `clearImmediate()`, `setInterval()`, `clearInterval()`, `setTimeout()`, `clearTimeout()` with an implementation that gets its time from the fake clock.
+
+In Node environment `process.hrtime`, `process.nextTick()` and in JSDOM environment `requestAnimationFrame()`, `cancelAnimationFrame()`, `requestIdleCallback()`, `cancelIdleCallback()` will be replaced as well.
+
+Configuration options:
+
+```ts
+type FakeableAPI =
+  | 'Date'
+  | 'hrtime'
+  | 'nextTick'
+  | 'performance'
+  | 'queueMicrotask'
+  | 'requestAnimationFrame'
+  | 'cancelAnimationFrame'
+  | 'requestIdleCallback'
+  | 'cancelIdleCallback'
+  | 'setImmediate'
+  | 'clearImmediate'
+  | 'setInterval'
+  | 'clearInterval'
+  | 'setTimeout'
+  | 'clearTimeout';
+
+type FakeTimersConfig = {
+  /**
+   * If set to `true` all timers will be advanced automatically by 20 milliseconds
+   * every 20 milliseconds. A custom time delta may be provided by passing a number.
+   * The default is `false`.
+   */
+  advanceTimers?: boolean | number;
+  /**
+   * List of names of APIs that should not be faked. The default is `[]`, meaning
+   * all APIs are faked.
+   */
+  doNotFake?: Array<FakeableAPI>;
+  /**
+   * Use the old fake timers implementation instead of one backed by `@sinonjs/fake-timers`.
+   * The default is `false`.
+   */
+  legacyFakeTimers?: boolean;
+  /** Sets current system time to be used by fake timers. The default is `Date.now()`. */
+  now?: number | Date;
+  /**
+   * The maximum number of recursive timers that will be run when calling `jest.runAllTimers()`.
+   * The default is `100_000` timers.
+   */
+  timerLimit?: number;
+};
+```
+
+Calling `jest.useFakeTimers()` will use fake timers for all tests within the file, until original timers are restored with `jest.useRealTimers()`.
+
+You can call `jest.useFakeTimers()` or `jest.useRealTimers()` from anywhere: top level, inside an `test` block, etc. Keep in mind that this is a **global operation** and will affect other tests within the same file. Calling `jest.useFakeTimers()` once again in the same test file would reset the internal state (e.g. timer count) and reinstall fake timers using the provided options:
+
+```js
+test('advance the timers automatically', () => {
+  jest.useFakeTimers({advanceTimers: true});
+  // ...
+});
+
+test('do not advance the timers and do not fake `performance`', () => {
+  jest.useFakeTimers({doNotFake: ['performance']});
+  // ...
+});
+
+test('uninstall fake timers for the rest of tests in the file', () => {
+  jest.useRealTimers();
+  // ...
+});
+```
+
+:::info Legacy Fake Timers
+
+For some reason you might have to use legacy implementation of fake timers. It can be enabled like this (additional options are not supported):
+
+```js
+jest.useFakeTimers({
+  legacyFakeTimers: true,
+});
+```
+
+Legacy fake timers will swap out `setImmediate()`, `clearImmediate()`, `setInterval()`, `clearInterval()`, `setTimeout()`, `clearTimeout()` with Jest [mock functions](MockFunctionAPI.md). In Node environment `process.nextTick()` and in JSDOM environment `requestAnimationFrame()`, `cancelAnimationFrame()` will be also replaced.
+
+:::
 
 Returns the `jest` object for chaining.
 
 ### `jest.useRealTimers()`
 
-Instructs Jest to use the real versions of the standard timer functions.
+Instructs Jest to restore the original implementations of the global date, performance, time and timer APIs. For example, you may call `jest.useRealTimers()` inside `afterEach` hook to restore timers after each test:
+
+```js
+afterEach(() => {
+  jest.useRealTimers();
+});
+
+test('do something with fake timers', () => {
+  jest.useFakeTimers();
+  // ...
+});
+
+test('do something with real timers', () => {
+  // ...
+});
+```
 
 Returns the `jest` object for chaining.
 
@@ -662,7 +761,11 @@ 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
+:::info
+
+This function is only available when using legacy fake timers implementation.
+
+:::
 
 ### `jest.advanceTimersByTime(msToRun)`
 
@@ -696,13 +799,21 @@ Returns the number of fake timers still left to run.
 
 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
+:::info
+
+This function is not available when using legacy 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
+:::info
+
+This function is not available when using legacy fake timers implementation.
+
+:::
 
 ## Misc