vitest-testing

Vitest is a unit testing framework for Node.js that uses a vitest.config.ts file to configure test environments, reporters, and coverage settings. Create a config file, write tests using describe and it blocks, then run the test suite with the vitest command to execute all tests concurrently.

Vitest provides vi.mock and vi.fn utilities to mock modules and individual functions. Use vi.mock at the top of test files to replace module implementations, and vi.fn to create spy functions that track calls and return values, enabling isolated unit tests.

Vitest's coverage configuration in vitest.config.ts enforces minimum coverage percentages across lines, functions, branches, and statements. Set thresholds in the coverage object to fail test runs when coverage drops below specified levels, ensuring comprehensive test quality.

Vitest snapshots capture expected output from functions or components and compare against future runs to detect unintended changes. Use toMatchSnapshot assertions to save baseline snapshots, then review diffs when snapshots fail to catch regressions.

Vitest provides test environment setup files to configure global state, mocks, and fixtures, plus concurrent execution with test isolation to prevent state leakage between tests. Type testing capabilities verify TypeScript type definitions and inference patterns.