advanced-js-mocking-patterns

Module mocking in Jest and Vitest uses jest.mock or vi.mock to replace dependencies with controlled implementations, isolating units and ensuring deterministic test behavior across code paths.

Partial mocking with spies verifies interactions without full module replacements. This testing pattern tracks function calls and arguments while preserving original logic, ensuring maintainable test implementations across unit and integration tests.

Fake timers control time progression in Vitest by replacing real clock functions with controllable mocks. This enables deterministic testing of time-dependent logic, ensuring correct handling of delays and timeouts without actual waiting.

Mock lifecycle management uses setup and teardown hooks to reset or restore mocks between tests. This prevents state leakage and cross-test contamination, reducing flaky tests and ensuring deterministic results across suites.

Yes, custom mock implementations simulate complex network request flows without real network calls. They allow precise control over success and failure paths, ensuring correct handling of edge cases and deterministic test outcomes.

Yes, these mocking patterns apply to both frontend and backend test suites. They support module mocks, spies, and fake timers across unit and integration tests, ensuring comprehensive mock lifecycle management and deterministic results.