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@jest/fake-timers
Advanced tools
@jest/fake-timers is a package that provides fake timer functions for Jest, a popular JavaScript testing framework. It allows you to control the passage of time in your tests, making it easier to test code that relies on timers, such as setTimeout, setInterval, and Date.
Mocking setTimeout and setInterval
This feature allows you to mock setTimeout and setInterval functions, enabling you to control the passage of time in your tests. The code sample demonstrates how to use jest.useFakeTimers() to mock the timers and jest.advanceTimersByTime() to fast-forward time.
const { jest } = require('@jest/globals');
jest.useFakeTimers();
setTimeout(() => {
console.log('This will be logged after 1 second');
}, 1000);
jest.advanceTimersByTime(1000); // Fast-forward time by 1 second
// Output: 'This will be logged after 1 second'
Mocking Date
This feature allows you to mock the Date object, enabling you to control the current date and time in your tests. The code sample demonstrates how to use jest.useFakeTimers('modern') to mock the Date object and jest.setSystemTime() to set a specific date and time.
const { jest } = require('@jest/globals');
jest.useFakeTimers('modern');
const now = Date.now();
console.log(now); // Outputs the current timestamp
jest.setSystemTime(new Date('2020-01-01'));
const newNow = Date.now();
console.log(newNow); // Outputs the timestamp for 2020-01-01
Clearing timers
This feature allows you to clear mocked timers, ensuring that the associated callbacks are not executed. The code sample demonstrates how to use clearTimeout() to clear a setTimeout timer.
const { jest } = require('@jest/globals');
jest.useFakeTimers();
const timeoutId = setTimeout(() => {
console.log('This will not be logged');
}, 1000);
clearTimeout(timeoutId);
jest.advanceTimersByTime(1000); // Fast-forward time by 1 second
// No output
Sinon is a popular standalone test spies, stubs, and mocks library for JavaScript. It provides similar functionalities to @jest/fake-timers, including the ability to mock timers and control the passage of time. However, Sinon is not tied to any specific testing framework and can be used with various testing libraries.
Lolex is a standalone library for creating fake timers and controlling the passage of time. It provides similar functionalities to @jest/fake-timers, such as mocking setTimeout, setInterval, and Date. Lolex can be used independently or integrated with other testing frameworks.
28.1.1
[jest]
Expose Config
type (#12848)[@jest/reporters]
Improve GitHubActionsReporter
s annotation format (#12826)[@jest/types]
Infer argument types passed to test
and describe
callback functions from each
tables (#12885, #12905)[@jest/expect-utils]
Fix deep equality of ImmutableJS OrderedMaps (#12899)[jest-docblock]
Handle multiline comments in parseWithComments (#12845)[jest-mock]
Improve spyOn
error messages (#12901)[jest-runtime]
Correctly report V8 coverage with resetModules: true
(#12912)[jest-worker]
Make JestWorkerFarm
helper type to include methods of worker module that take more than one argument (#12839)FAQs
Unknown package
The npm package @jest/fake-timers receives a total of 21,764,378 weekly downloads. As such, @jest/fake-timers popularity was classified as popular.
We found that @jest/fake-timers demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 3 open source maintainers collaborating on the project.
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