javascript-typescript-jest

Jest testing best practices for JavaScript and TypeScript projects with mocking, async handling, and React patterns. - Organize tests with descriptive names in nested describe blocks, using .test.ts / .test.js files placed alongside source code or in __tests__ directories - Mock external dependencies with jest.mock() , jest.spyOn() , and mockImplementation() , resetting between tests to prevent state leakage - Handle async code with promises, async/await , and resolves / rejects matchers; set timeouts for slow tests - Test React components with React Testing Library, querying by accessibility roles and labels, and using userEvent for realistic interactions - Includes 20+ common matchers covering truthiness, numbers, strings, arrays, objects, exceptions, and mock function assertions - 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', () => {}) }) - 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...