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vitest-testing AI Agent Skill
View Source: oakoss/agent-skills
SafeInstallation
npx skills add oakoss/agent-skills --skill vitest-testing 66
Installs
Vitest Testing
Overview
Vitest is a Vite-native unit testing framework that shares the same configuration and plugin ecosystem. Built for speed with native ESM support, hot module replacement for tests, and parallel execution.
When to use: Unit tests, component tests, integration tests, hook tests, in-source tests. Testing React components with React Testing Library. Testing TanStack Query/Router/Form patterns.
When NOT to use: End-to-end testing (use Playwright), visual regression testing (use Percy/Chromatic), load testing (use k6).
Quick Reference
| Pattern | API | Key Points |
|---|---|---|
| Test structure | describe('suite', () => {}) |
Organize related tests |
| Single test | test('behavior', () => {}) or it() |
Both are aliases |
| Parameterized tests | test.each([...])('name', (arg) => {}) |
Run same test with different inputs |
| Concurrent tests | test.concurrent('name', async () => {}) |
Run tests in parallel |
| Skip test | test.skip('name', () => {}) or skipIf(cond) |
Conditionally skip tests |
| Only test | test.only('name', () => {}) |
Run specific test for debugging |
| Assertions | expect(value).toBe(expected) |
Compare primitive values |
| Deep equality | expect(obj).toEqual(expected) |
Compare objects/arrays |
| Async assertions | await expect(promise).resolves.toBe(value) |
Test promise resolution |
| Before each test | beforeEach(() => {}) |
Setup before each test |
| After each test | afterEach(() => {}) |
Cleanup after each test |
| Mock function | vi.fn() |
Create spy function |
| Mock module | vi.mock('./module') |
Replace entire module |
| Spy on method | vi.spyOn(obj, 'method') |
Track calls to existing method |
| Clear mocks | vi.clearAllMocks() |
Clear call history |
| Fake timers | vi.useFakeTimers() |
Control setTimeout/setInterval |
| Render component | render(<Component />) |
Mount React component for testing |
| Query by role | screen.getByRole('button') |
Find elements by accessibility role |
| User interaction | await user.click(element) |
Simulate user events |
| Wait for change | await waitFor(() => expect(...)) |
Wait for async changes |
| Find async element | await screen.findByText('text') |
Query + wait combined |
| Render hook | renderHook(() => useHook()) |
Test custom hooks |
| Update hook props | rerender(newProps) |
Re-render hook with new props |
| Snapshot | expect(value).toMatchSnapshot() |
Compare against saved snapshot |
| Inline snapshot | expect(value).toMatchInlineSnapshot() |
Snapshot stored in test file |
| CLI run once | vitest run |
Single run, no watch |
| Run changed tests | vitest --changed |
Tests affected by git changes |
| Filter by name | vitest -t "pattern" |
Grep test names |
| Soft assertions | expect.soft(value).toBe(x) |
Continue on failure, collect all |
| Poll assertions | await expect.poll(() => val).toBe(x) |
Retry until passing |
| Test fixtures | const test = base.extend<F>({...}) |
Reusable setup via test.extend |
| Hoisted mocks | vi.hoisted(() => ({ fn: vi.fn() })) |
Variables for vi.mock factory |
| Shard tests | vitest --shard 1/3 |
Split across CI workers |
| Tags | test('name', { tags: ['slow'] }, ...) |
Filter with --tags-filter |
| Stub globals | vi.stubGlobal('fetch', vi.fn()) |
Replace global objects cleanly |
Common Mistakes
| Mistake | Correct Pattern |
|---|---|
Using getBy for async content |
Use findBy or waitFor for async |
| Testing implementation details | Test behavior and public API |
Using getByTestId as first choice |
Prefer getByRole, getByLabelText, getByText |
Missing userEvent.setup() |
Always call const user = userEvent.setup() first |
| Shared state between tests | Use beforeEach to reset or create fresh instances |
| Not cleaning up mocks | Use vi.clearAllMocks() in afterEach |
| Mocking too much | Only mock external dependencies and APIs |
| Not disabling retries in tests | Set retry: false for TanStack Query tests |
| Immediate assertions on async | Use await waitFor() or findBy queries |
| Creating QueryClient in render | Create once in wrapper or use useState |
| Testing library code | Trust the library, test your usage |
| Not awaiting user events | All user.* methods return promises |
Using act manually |
userEvent and Testing Library handle this |
| Inline select without memoization | Extract to stable function for TanStack Query |
| Variables in vi.mock factory | Use vi.hoisted() to declare mock variables |
Single expect for multiple checks |
Use expect.soft() to collect all failures |
setTimeout in tests for async waits |
Use expect.poll() or vi.waitFor() |
Manual beforeEach for reusable setup |
Use test.extend fixtures for composable setup |
Delegation
- Test discovery: For finding untested code paths, use
Exploreagent - Coverage analysis: For full coverage review, use
Taskagent - E2E testing: If
playwrightskill is available, delegate E2E testing to it - Code review: After writing tests, delegate to
code-revieweragent
References
- Test fundamentals: structure, assertions, lifecycle hooks
- Mocking: vi.fn, vi.mock, vi.spyOn, module mocking
- Component testing: React Testing Library, queries, user-event
- Hook testing: renderHook, async hooks, TanStack patterns
- Test setup: jest-dom matchers, cleanup, custom render, MSW, polyfills
- Configuration: vitest.config.ts, workspace, coverage, reporters
- Advanced patterns: snapshots, concurrent tests, in-source, type testing
- CLI and filtering: commands, watch mode, tags, sharding
- Fixtures and context: test.extend, scoping, auto fixtures, injection
Installs
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View Source
oakoss/agent-skills
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How to use this skill
Install vitest-testing by running npx skills add oakoss/agent-skills --skill vitest-testing in your project directory. Run the install command above in your project directory. The skill file will be downloaded from GitHub and placed in your project.
No configuration needed. Your AI agent (Claude Code, Cursor, Windsurf, etc.) automatically detects installed skills and uses them as context when generating code.
The skill enhances your agent's understanding of vitest-testing, helping it follow established patterns, avoid common mistakes, and produce production-ready output.
What you get
Skills are plain-text instruction files — not executable code. They encode expert knowledge about frameworks, languages, or tools that your AI agent reads to improve its output. This means zero runtime overhead, no dependency conflicts, and full transparency: you can read and review every instruction before installing.
Compatibility
This skill works with any AI coding agent that supports the skills.sh format, including Claude Code (Anthropic), Cursor, Windsurf, Cline, Aider, and other tools that read project-level context files. Skills are framework-agnostic at the transport level — the content inside determines which language or framework it applies to.
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