jest-watcher

What is jest-watcher?

The jest-watcher package is a part of the Jest ecosystem and is used to implement custom watch plugins for Jest. It provides an API to create plugins that can hook into Jest's watch mode, allowing developers to add custom watch behaviors to their test suites.

What are jest-watcher's main functionalities?

Custom Watch Plugins

This feature allows developers to create custom watch plugins that can react to file changes, determine if a test suite should run, and more. The code sample shows a basic structure of a custom watch plugin.

class MyCustomPlugin {
  apply(jestHooks) {
    jestHooks.onFileChange(({ projects }) => {
      console.log('Files changed:', projects[0].changedFiles);
    });
    jestHooks.shouldRunTestSuite(() => true);
  }
}

module.exports = MyCustomPlugin;

Interactive Watch Plugins

This feature allows the creation of interactive watch plugins that can provide custom interactive CLI interfaces during Jest's watch mode. The code sample demonstrates how to implement an interactive behavior that filters tests based on a pattern.

class MyInteractivePlugin {
  run(globalConfig, updateConfigAndRun) {
    // Implement interactive behavior here
    updateConfigAndRun({
      testNamePattern: 'pattern to filter tests'
    });
    return Promise.resolve();
  }
}

module.exports = MyInteractivePlugin;

Other packages similar to jest-watcher

mocha-watch

Mocha-watch is a watch mode for Mocha testing framework. It provides similar functionality to jest-watcher by re-running tests when file changes are detected. However, it is tailored for Mocha and does not offer the same plugin API for extending watch behavior.

karma

Karma is a test runner that works with multiple testing frameworks like Jasmine, Mocha, and QUnit. It can watch files and re-run tests on changes, similar to jest-watcher. Karma is more of a full-fledged test runner with a focus on running tests in different browsers, whereas jest-watcher is specifically for creating watch plugins in Jest.

ava

AVA is a test runner with built-in watch mode functionality. It automatically re-runs tests when it detects changes. AVA's watch mode is not plugin-based like jest-watcher, but it offers a simple and fast out-of-the-box solution for watching tests without the need for additional configuration.

README

The README file is missing

Changelog

25.5.0

Features

• [@jest/globals] New package so Jest's globals can be explicitly imported (#9801)
• [jest-core] Show coverage of sources related to tests in changed files (#9769)
• [jest-runtime] Populate require.cache (#9841)

Fixes

• [*] Use graceful-fs directly in every package instead of relying on fs being monkey patched (#9443)
• [expect] Prints the Symbol name into the error message with a custom asymmetric matcher (#9888)
• [jest-circus, jest-jasmine2] Support older version of jest-runtime (#9903 & #9842)
• [@jest/environment] Make sure not to reference Jest types (#9875)
• [jest-message-util] Code frame printing should respect --noStackTrace flag (#9866)
• [jest-runtime] Support importing CJS from ESM using import statements (#9850)
• [jest-runtime] Support importing parallel dynamic imports (#9858)
• [jest-transform] Improve source map handling when instrumenting transformed code (#9811)

Chore & Maintenance

• [docs] Add an example for mocking non-default export class

Performance

• [jest-resolve] Update resolve to a version using native realpath, which is faster than the default JS implementation (#9872)
• [jest-resolve] Pass custom cached realpath function to resolve (#9873)
• [jest-runtime] Add teardown method to clear any caches when tests complete (#9906)
• [jest-runtime] Do not pass files required internally through transformation when loading them (#9900)
• [jest-runtime] Use Maps instead of object literals as cache holders (#9901)