mocking-strategies

To mock external API calls in Vitest unit tests, you can use `vi.fn()` to create stubs or `vi.mock()` to replace the module making the network request, allowing you to test function logic without actual network requests.

The best way to mock Node.js modules and npm packages in Vitest is using `vi.mock()` to replace module implementations with test doubles, ensuring your unit tests remain isolated from external dependencies.

Use `vi.spyOn()` to track method calls on existing objects without changing behavior, and `vi.fn()` to create standalone mock functions or stubs. Both provide mock assertions for effective JavaScript unit testing.

Yes, you can mock timers in Vitest for JavaScript and TypeScript projects. Vitest provides timer mocking strategies to control time-dependent logic, ensuring reliable and isolated unit tests for asynchronous operations.

You assert mock calls and return values in Vitest unit testing by utilizing the assertion properties attached to `vi.fn()` and `vi.spyOn()` test doubles. This verifies that your units interact with dependencies exactly as expected.