johnnystefan/vitest

For E2E tests: Use playwright skill. This skill covers unit/integration tests with Vitest + React Testing Library.

Test Structure (REQUIRED)

Use Given/When/Then (AAA) pattern with comments:

it("should update user name when form is submitted", async () => {
  // Given - Arrange
  const user = userEvent.setup();
  const onSubmit = vi.fn();
  render(<UserForm onSubmit={onSubmit} />);

  // When - Act
  await user.type(screen.getByLabelText(/name/i), "John");
  await user.click(screen.getByRole("button", { name: /submit/i }));

  // Then - Assert
  expect(onSubmit).toHaveBeenCalledWith({ name: "John" });
});

---

Describe Block Organization

describe('ComponentName', () => {
  describe('when [condition]', () => {
    it('should [expected behavior]', () => {});
  });
});

Group by behavior, NOT by method.

---

Query Priority (REQUIRED)

| Priority | Query | Use Case | | -------- | ---------------------- | ------------------------- | | 1 | getByRole | Buttons, inputs, headings | | 2 | getByLabelText | Form fields | | 3 | getByPlaceholderText | Inputs without label | | 4 | getByText | Static text | | 5 | getByTestId | Last resort only |

// ✅ GOOD
screen.getByRole('button', { name: /submit/i });
screen.getByLabelText(/email/i);

// ❌ BAD
container.querySelector('.btn-primary');

---

userEvent over fireEvent (REQUIRED)

// ✅ ALWAYS use userEvent
const user = userEvent.setup();
await user.click(button);
await user.type(input, 'hello');

// ❌ NEVER use fireEvent for interactions
fireEvent.click(button);

---

Async Testing Patterns

// ✅ findBy for elements that appear async
const element = await screen.findByText(/loaded/i);

// ✅ waitFor for assertions
await waitFor(() => {
  expect(screen.getByText(/success/i)).toBeInTheDocument();
});

// ✅ ONE assertion per waitFor
await waitFor(() => expect(mockFn).toHaveBeenCalled());
await waitFor(() => expect(screen.getByText(/done/i)).toBeVisible());

// ❌ NEVER multiple assertions in waitFor
await waitFor(() => {
  expect(mockFn).toHaveBeenCalled();
  expect(screen.getByText(/done/i)).toBeVisible(); // Slower failures
});

---

Mocking

// Basic mock
const handleClick = vi.fn();

// Mock with return value
const fetchUser = vi.fn().mockResolvedValue({ name: 'John' });

// Always clean up
afterEach(() => {
  vi.restoreAllMocks();
});

vi.spyOn vs vi.mock

| Method | When to Use | | ---------- | ------------------------------------- | | vi.spyOn | Observe without replacing (PREFERRED) | | vi.mock | Replace entire module (use sparingly) |

---

Common Matchers

// Presence
expect(element).toBeInTheDocument();
expect(element).toBeVisible();

// State
expect(button).toBeDisabled();
expect(input).toHaveValue('text');
expect(checkbox).toBeChecked();

// Content
expect(element).toHaveTextContent(/hello/i);
expect(element).toHaveAttribute('href', '/home');

// Functions
expect(fn).toHaveBeenCalledWith(arg1, arg2);
expect(fn).toHaveBeenCalledTimes(2);

---

What NOT to Test

// ❌ Internal state
expect(component.state.isLoading).toBe(true);

// ❌ Third-party libraries
expect(axios.get).toHaveBeenCalled();

// ❌ Static content (unless conditional)
expect(screen.getByText('Welcome')).toBeInTheDocument();

// ✅ User-visible behavior
expect(screen.getByRole('button')).toBeDisabled();

---

File Organization

components/
├── Button/
│   ├── Button.tsx
│   ├── Button.test.tsx    # Co-located
│   └── index.ts

---

Commands

pnpm test                    # Watch mode
pnpm test:run               # Single run
pnpm test:coverage          # With coverage
pnpm test Button            # Filter by name