react-testing

Tests React 19 components with Testing Library and Vitest: user-centric queries prioritized by accessibility (`getByRole` first, `getByTestId` last resort), `userEvent` for realistic interactions (never `fireEvent`), `findBy`/`waitFor` for async assertions (never `setTimeout`), and MSW for API mocking (never direct fetch mocking).

Also covers testing React 19 features (useActionState, use()), custom hooks, Suspense boundaries, error boundaries, and accessibility audits with axe-core. Provides Vitest configuration and 9 ready-to-copy test templates. This is a testing-methodology skill layered on top of the React skills (react-19, react-state, react-forms) — it doesn't teach those APIs themselves, only how to test components that use them.

React Testing Library

Test React components the way users interact with them.

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Analyze existing test patterns
2. fuse-ai-pilot:research-expert - Verify latest Testing Library docs via Context7/Exa
3. mcp__context7__query-docs - Check userEvent, waitFor patterns

After implementation, run fuse-ai-pilot:sniper for validation.

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Overview

When to Use

• Testing React component behavior
• Validating user interactions
• Ensuring accessibility compliance
• Mocking API calls with MSW
• Testing custom hooks
• Testing React 19 features (useActionState, use())

Why React Testing Library

Feature	Benefit
User-centric	Tests what users see
Accessible queries	Encourages a11y markup
No implementation details	Resilient to refactoring
Vitest integration	10-20x faster than Jest

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Critical Rules

1. Query by role first - getByRole is most accessible
2. Use userEvent, not fireEvent - Realistic interactions
3. waitFor for async - Never setTimeout
4. MSW for API mocking - Don't mock fetch
5. Test behavior, not implementation - No internal state testing

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Reference Guide

Concepts

Topic	Reference
Setup & installation	references/installation.md
Query priority	references/queries.md
User interactions	references/user-events.md
Async patterns	references/async-testing.md
API mocking	references/msw-setup.md
React 19 hooks	references/react-19-hooks.md
Accessibility	references/accessibility-testing.md
Custom hooks	references/hooks-testing.md
Vitest config	references/vitest-config.md
Mocking patterns	references/mocking-patterns.md

Templates

Template	Use Case
templates/basic-setup.md	Vitest + RTL + MSW config
templates/component-basic.md	Simple component tests
templates/component-async.md	Loading/error/success
templates/form-testing.md	Forms + useActionState
templates/hook-basic.md	Custom hook tests
templates/api-integration.md	MSW integration tests
templates/suspense-testing.md	Suspense + use()
templates/error-boundary.md	Error boundary tests
templates/accessibility-audit.md	axe-core a11y audit

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Forbidden Patterns

Pattern	Reason	Alternative
fireEvent	Not realistic	userEvent
setTimeout	Flaky	waitFor, findBy
getByTestId first	Not accessible	getByRole
Direct fetch mocking	Hard to maintain	MSW
Empty waitFor	No assertion	Add expect()

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Quick Start

Install

npm install -D vitest @testing-library/react \
  @testing-library/user-event @testing-library/jest-dom \
  jsdom msw

→ See templates/basic-setup.md for complete configuration

Basic Test

import { render, screen } from '@testing-library/react'
import userEvent from '@testing-library/user-event'

test('button click works', async () => {
  const user = userEvent.setup()
  render(<Button onClick={fn}>Click</Button>)

  await user.click(screen.getByRole('button'))

  expect(fn).toHaveBeenCalled()
})

→ See templates/component-basic.md for more examples

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Best Practices

Query Priority

1. getByRole - Buttons, headings, inputs
2. getByLabelText - Form inputs
3. getByText - Static text
4. getByTestId - Last resort

Async Pattern

// Preferred: findBy
await screen.findByText('Loaded')

// Alternative: waitFor
await waitFor(() => expect(...).toBeInTheDocument())

→ See templates/component-async.md

userEvent Setup

const user = userEvent.setup()
await user.click(button)
await user.type(input, 'text')

→ See references/user-events.md