writing-vitest-tests

Vitest tests use describe blocks to organize related test cases and test blocks for individual assertions. Structure your test file by importing Vitest, wrapping related tests in describe, and using test or it to define each case with expect assertions.

Vitest provides vi.fn() to create mock functions and vi.mock() to mock modules. Use vi.fn() to track calls and return values, then assert on mock behavior with expect(mockFn).toHaveBeenCalled() or similar matchers.

Yes, Vitest supports async testing by using async/await in test functions or returning promises. Mark your test callback as async and await promises, or return the promise directly for Vitest to handle completion.

Organize tests using describe blocks by module or feature, apply setup and teardown with beforeEach and afterEach hooks, and use parameterized tests for data-driven cases to reduce duplication and improve readability.

Vitest supports both JavaScript and TypeScript natively. Write tests in either language using the same APIs—describe, test, expect, and vi mocking—with full type support in TypeScript test files.

Vitest includes expect assertions for value matching (toBe, toEqual), truthiness (toBeTruthy), exceptions (toThrow), and mock calls (toHaveBeenCalled). Combine matchers for precise test validation across unit and integration scenarios.