testing

Unit tests validate individual functions or modules by checking their behavior against expected outputs. With Vitest, create .test.ts or .test.tsx files alongside your code, use describe and it blocks to organize tests, and run them via bunx vitest run. This ensures code reliability and catches regressions early.

Mocking in Vitest isolates units under test by replacing external dependencies with controlled substitutes. Define mocks using vi.mock() or vi.fn() before tests run, then verify calls and return values. This prevents side effects and speeds up test execution across your test suite.

Test coverage reports identify which lines, branches, and functions lack test validation. Run Vitest with coverage flags to generate metrics, then review the report to spot untested code paths and edge cases. Higher coverage reduces bugs in production and increases confidence in refactoring.

Vitest handles async operations by returning promises from test functions or using async/await syntax. Tests automatically wait for async operations to complete before asserting results, allowing you to validate callbacks, promises, and async functions reliably.

Vitest integrates directly into TypeScript and JavaScript projects with minimal setup. Install Vitest, place test files alongside source code following naming conventions, and run tests immediately. No additional configuration is required for basic unit and integration testing.

Describe blocks group related tests logically, improving readability and test organization. Structure tests by module or feature, nest describes for hierarchical organization, and use clear naming that mirrors your codebase. This makes test output scannable and maintenance easier as projects grow.