Courses / Frontend Testing
12. Typing Jest mocks in TypeScript
Correctly typing jest.fn, jest.Mocked, and mocked modules to get type-safe tests.
JavaScript / TypeScript
Typing Jest mocks in TypeScript
How to give accurate TypeScript types to jest.fn, jest.Mocked, and mocked modules so tests are type-safe.
"I want my mocks to match the real API so refactors fail the tests at compile time, not at runtime."
Use TypeScript helpers and proper typings (jest.fn with generics, jest.Mocked<T>, and ts-jest/mock utilities) so mocked functions and modules preserve argument and return types for safe assertions.
"I want my mocks to match the real API so refactors fail the tests at compile time, not at runtime."
Use TypeScript helpers and proper typings (jest.fn with generics, jest.Mocked<T>, and ts-jest/mock utilities) so mocked functions and modules preserve argument and return types for safe assertions.