jest-runner

What is jest-runner?

The jest-runner npm package is a custom runner for Jest that allows you to run tests with a specified test runner. It is part of the Jest ecosystem and is used to execute tests written for Jest in a customizable environment. It can be used to run tests in parallel, to specify custom test environments, and to integrate with other testing tools and frameworks.

What are jest-runner's main functionalities?

Running tests in parallel

By default, Jest runs all tests in parallel, which can speed up the test execution time. However, if you need to run tests serially (one after another), you can use the `--runInBand` or `-i` option. This is useful when tests are not isolated and may interfere with each other when run in parallel.

jest --runInBand

Custom test environments

Jest allows you to specify a custom test environment for your tests. By setting the `testEnvironment` option in your Jest configuration, you can choose the environment in which your tests will run, such as `node` for a Node.js environment or `jsdom` for a browser-like environment. The `runner` option can be set to `jest-runner` to use it as the test runner.

module.exports = {
  testEnvironment: 'node',
  runner: 'jest-runner'
};

Integrating with other testing tools

Jest-runner can be extended to integrate with other testing tools and frameworks. For example, `jest-runner-eslint` allows you to run ESLint as a Jest test, providing a unified testing and linting workflow. You can configure Jest to use different runners for different types of tests or files, and you can also add watch plugins to enhance the developer experience during watch mode.

module.exports = {
  runner: 'jest-runner-eslint',
  displayName: 'lint',
  testMatch: ['<rootDir>/src/**/*.js'],
  watchPlugins: [
    'jest-watch-typeahead/filename',
    'jest-watch-typeahead/testname',
  ]
};

Other packages similar to jest-runner

mocha

Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple. It is similar to Jest in that it provides a test running environment, but it has a different API and requires manual configuration of assertion libraries, mocking, and spying tools.

jasmine

Jasmine is a behavior-driven development framework for testing JavaScript code. It does not require a DOM and has a clean, obvious syntax so that you can easily write tests. It is similar to Jest but is considered less opinionated in terms of how tests are structured and executed.

ava

AVA is a test runner for Node.js with a concise API, detailed error output, and process isolation that lets you develop with confidence. AVA is similar to Jest-runner in that it can run tests in parallel, but it emphasizes minimalism and speed, and it does not provide a built-in mocking library.

karma

Karma is a test runner that works with any framework (such as Mocha, Jasmine, QUnit, and more), which makes it highly adaptable. It is designed to work with continuous integration tools and offers a plugin system. Unlike Jest, Karma is primarily used for running tests in actual browsers, which is useful for testing browser-specific issues.

README

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