write-unit-tests

To write Vitest unit tests for utility functions, structure tests using the AAA pattern, apply vi.fn and vi.spyOn for mocking, and validate edge cases like empty inputs or boundary values.

Fake timer handling in Vitest utility tests involves mocking time-dependent functions to control execution, followed by strict cleanup of timers and mocks after each test to prevent state leakage.

The best way to mock browser APIs in Vitest is using vi.fn and vi.spyOn to intercept calls, allowing you to simulate API behaviors and validate edge cases while ensuring strict mock cleanup afterward.

Yes, you can use this approach to fix failing regression tests for shared utils by rewriting them with the AAA pattern and verifying edge cases or error paths to ensure coverage and stability.

You should enforce strict cleanup of mocks and timers after each test to prevent state leakage and cross-test contamination, ensuring that fake timers and mocked functions do not affect subsequent test results.