jest-patterns

Structure Jest and Vitest tests using describe blocks to group features and it blocks for scenarios, nesting describes for sub-scenarios with setup and teardown via beforeEach and afterEach. This standardizes test organization and improves consistency across JS and TS projects.

Mock modules and APIs in Jest and Vitest using jest.fn or vi.fn for functions, jest.mock or vi.mock for modules, and jest.spyOn or vi.spyOn for spies. This strategy ensures tests remain isolated and avoids real API calls to maintain reliability.

Test asynchronous code in Jest and Vitest using async and await within it blocks, or apply .resolves and .rejects matchers to promises. These async testing patterns ensure proper assertions are made before the test completes.

Yes, these Jest and Vitest testing patterns apply to unit and integration tests across JavaScript and TypeScript apps. They define expectations for test structure, mocking strategy, async handling, and recommended matchers suitable for both test types.

Use common matchers like toBe and toEqual for equality, toMatchObject for partial object matching, toMatchSnapshot for snapshots, and toHaveBeenCalledWith for mock verification. These matchers standardize expectations in Vitest and Jest test suites.

Unit tests must avoid real API calls in Jest and Vitest to promote isolated tests and prevent external dependencies from causing flaky results. Use mocking strategies like jest.mock or vi.mock to safely simulate API responses instead.