javascript-typescript-jest

par github

Bonnes pratiques de test Jest pour les projets JavaScript et TypeScript avec mocking, gestion asynchrone et patterns React. Organisez les tests avec des noms descriptifs dans des blocs describe imbriqués, en utilisant des fichiers .test.ts / .test.js placés à côté du code source ou dans des répertoires __tests__. Mockez les dépendances externes avec jest.mock(), jest.spyOn() et mockImplementation(), en réinitialisant entre les tests pour éviter les fuites d'état. Gérez le code asynchrone avec les promesses, async/await et les matchers resolves / rejects ; définissez...

npx skills add https://github.com/github/awesome-copilot --skill javascript-typescript-jest

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Test Structure

Name test files with .test.ts or .test.js suffix
Place test files next to the code they test or in a dedicated __tests__ directory
Use descriptive test names that explain the expected behavior
Use nested describe blocks to organize related tests
Follow the pattern: describe('Component/Function/Class', () => { it('should do something', () => {}) })

Effective Mocking

Mock external dependencies (APIs, databases, etc.) to isolate your tests
Use jest.mock() for module-level mocks
Use jest.spyOn() for specific function mocks
Use mockImplementation() or mockReturnValue() to define mock behavior
Reset mocks between tests with jest.resetAllMocks() in afterEach

Testing Async Code

Always return promises or use async/await syntax in tests
Use resolves/rejects matchers for promises
Set appropriate timeouts for slow tests with jest.setTimeout()

Snapshot Testing

Use snapshot tests for UI components or complex objects that change infrequently
Keep snapshots small and focused
Review snapshot changes carefully before committing

Testing React Components

Use React Testing Library over Enzyme for testing components
Test user behavior and component accessibility
Query elements by accessibility roles, labels, or text content
Use userEvent over fireEvent for more realistic user interactions

Common Jest Matchers

Basic: expect(value).toBe(expected), expect(value).toEqual(expected)
Truthiness: expect(value).toBeTruthy(), expect(value).toBeFalsy()
Numbers: expect(value).toBeGreaterThan(3), expect(value).toBeLessThanOrEqual(3)
Strings: expect(value).toMatch(/pattern/), expect(value).toContain('substring')
Arrays: expect(array).toContain(item), expect(array).toHaveLength(3)
Objects: expect(object).toHaveProperty('key', value)
Exceptions: expect(fn).toThrow(), expect(fn).toThrow(Error)
Mock functions: expect(mockFn).toHaveBeenCalled(), expect(mockFn).toHaveBeenCalledWith(arg1, arg2)