A test runner discovers test files, executes their tests, and reports successes, failures, and detected problems. Angular applications commonly use Karma or Jest, but Karma is deprecated while Jest has experimental official support from Angular v16. section 8.2.1
Table 8.1 Karma vs. Jest
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Karma
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Jest
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|---|---|
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Developed by the Angular team
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Developed by Facebook
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Runs in a real browser
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Runs in a NodeJS environment
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Has to spin up the browser itself and then run the tests inside it, sometimes resulting in slower performance
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Runs as an independent JS program, with no browser, and can be faster
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No need to mock the browser’s built-in functionality, as it already runs in a real browser
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We can’t directly use browser APIs here, as Jest runs in a NodeJS runtime; for instance, if our component calls
localStorage, we will have to mock it for the tests to run correctly
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Allows for cross-browser testing: if our application uses APIs that might not exist in some older browsers, we can configure Karma to use several different browsers and see if the tests pass on all of them
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No real cross-browser testing
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Compare Karma’s real-browser execution and cross-browser testing with Jest’s Node.js execution, speed, and need for browser API mocks. section 8.2.1
A Jest-based Angular setup typically involves:
- Discovering files ending in .spec.ts through tsconfig.spec.json. section 8.2.2
- Changing angular.json so the test target uses the Jest builder and the testing TypeScript configuration. section 8.2.2
- Installing Jest, jsdom, and Jest type definitions, then adding a setup file when custom configuration is required. section 8.2.2
- Rerunning ng test to verify that Jest executes the tests, while treating subsequent dependency-injection failures as separate test problems. section 8.2.2
Migrating an Angular test target
An HRMS application initially runs default Karma tests. Configure the test target for Jest, install its development dependencies, and rerun ng test. A changed reporting format confirms that Jest is active; a NullInjectorError for HttpClient still requires test-environment configuration or mocking. section 8.2.2
Runner choice remains a team decision. Jest is suitable for the current setup, while Web Test Runner represents a future browser-based option; Angular does not yet provide a stable supported default across these transitions. section 8.5
