jest-runner

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',
  ]
};