vitest-testing

# Vitest Best Practices ## Quick Reference ```ts import { describe, it, expect, beforeEach, vi } from 'vitest' describe('feature name', () => { beforeEach(() => { vi.clearAllMocks() }) it('should do something specific', () => { expect(actual).toBe(expected) }) it.todo('planned test') it.skip('temporarily disabled') it.only('run only this during dev') }) ``` ## Common Assertions ```ts // Equality expect(value).toBe(42) // Strict (===) expect(obj).toEqual({ a: 1 }) // Deep equality expect(obj).toStrictEqual({ a: 1 }) // Strict deep (checks types) // Truthiness expect(value).toBeTruthy() expect(value).toBeFalsy() expect(value).toBeNull() expect(value).toBeUndefined() // Numbers expect(0.1 + 0.2).toBeCloseTo(0.3) expect(value).toBeGreaterThan(5) // Strings/Arrays expect(str).toMatch(/pattern/) expect(str).toContain('substring') expect(array).toContain(item) expect(array).toHaveLength(3) // Objects expect(obj).toHaveProperty('key') expect(obj).toHaveProperty('nested.key', 'value') expect(obj).toMatchObject({ subset: 'of properties' }) // Exceptions expect(() => fn()).toThrow() expect(() => fn()).toThrow('error message') expect(() => fn()).toThrow(/pattern/) ``` ## Async Testing ```ts // Async/await (preferred) it('fetches data', async () => { const data = await fetchData() expect(data).toEqual({ id: 1 }) }) // Promise matchers - ALWAYS await these await expect(fetchData()).resolves.toEqual({ id: 1 }) await expect(fetchData()).rejects.toThrow('Error') // Wrong - creates false positive expect(promise).resolves.toBe(value) // Missing await! ``` ## Quick Mock Reference ```ts const mockFn = vi.fn() mockFn.mockReturnValue(42) mockFn.mockResolvedValue({ data: 'value' }) expect(mockFn).toHaveBeenCalled() expect(mockFn).toHaveBeenCalledWith('arg1', 'arg2') expect(mockFn).toHaveBeenCalledTimes(2) ``` ## Additional Documentation - **Mocking**: See [references/mocking.md](references/mocking.md) for module mocking, spying, cleanup - **Configuration**: See [references/config.md](references/config.md) for vitest.config, setup files, coverage - **Patterns**: See [references/patterns.md](references/patterns.md) for timers, snapshots, anti-patterns ## Test Methods Quick Reference | Method | Purpose | |--------|---------| | `it()` / `test()` | Define test | | `describe()` | Group tests | | `beforeEach()` / `afterEach()` | Per-test hooks | | `beforeAll()` / `afterAll()` | Per-suite hooks | | `.skip` | Skip test/suite | | `.only` | Run only this | | `.todo` | Placeholder | | `.concurrent` | Parallel execution | | `.each([...])` | Parameterized tests |