vitest-mocking

To mock a module in Vitest, you use the vi.mock function to replace the module's exports with test doubles. This isolates the unit under test by intercepting named or default imports and substituting controlled behavior.

The best way to stub globals like fetch and Date in Vitest is using vi.stubGlobal to replace them with test doubles. This allows you to control external interactions and time-based logic for reliable, repeatable tests.

Vitest mock hoisting causes errors because vi.mock is lifted to the top of the file before imports execute, breaking variable references. You must use inline mocks or factory functions to avoid scope and hoisting issues.

You verify mock calls in Vitest by using assertion methods like toHaveBeenCalledWith on your mocked functions or spies. This checks that your unit under test interacted with dependencies exactly as expected.

Yes, you can create test doubles for composables and utilities in Vitest by mocking their module imports or stubbing global dependencies. This ensures components and hooks are tested in isolation with controlled behavior.

You should clean up mocks across test suites in Vitest after each test to prevent state leakage. Restoring mocks and stubs ensures every test runs in isolation and produces reliable, repeatable results.