javascript-typescript-jest

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()