javascript-typescript-jest

作成者： github

Jestテストのベストプラクティス：JavaScriptおよびTypeScriptプロジェクトにおけるモック、非同期処理、Reactパターン。テストは説明的な名前を付けてネストされたdescribeブロックで整理し、.test.ts / .test.jsファイルをソースコードと並べて配置するか、__tests__ディレクトリに配置します。外部依存関係はjest.mock()、jest.spyOn()、mockImplementation()でモック化し、テスト間でリセットして状態の漏洩を防ぎます。非同期コードはPromise、async/await、resolves/rejectsマッチャーで処理し、設定...

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)