testing

Vitest organizes tests in .test.ts or .test.tsx files placed alongside the module under test. Write test suites using describe blocks and individual tests with it(), following clear naming conventions. Run tests with bunx vitest run --silent='passed-only' to verify passing tests and establish reliable, readable test structure.

Vitest provides vi.spyOn() for spying on specific methods and vi.mock() for isolating entire modules. These strategies prevent tests from depending on external state, ensure tests run independently, and reduce flakiness by controlling side effects and external calls.

Vitest enables debugging through structured test output and coverage reporting. Use test organization patterns to identify failures quickly, apply mocking strategies to isolate problems, and measure coverage expectations to identify untested code paths and strengthen reliability.

Vitest supports TDD workflows by enabling fast test execution and incremental test improvements. Write tests before implementation, run them frequently to guide development, and leverage mocking to define contracts before writing production code.

Vitest works with both JavaScript and TypeScript projects. It handles .test.ts, .test.tsx, and equivalent JavaScript test files, supporting mixed-language codebases with the same test structure, mocking, and coverage capabilities across both languages.

Flaky tests often result from poor isolation, missing mocks, or unclear test organization. Vitest best practices prescribe explicit mocking strategies, proper setup and teardown patterns, and clear naming conventions to maintain reliable tests and reduce debugging time.