SKILL.md

name	vitest
description	Vitest unit testing patterns with React Testing Library. Trigger: When writing unit tests for React components, hooks, or utilities.
license	Apache-2.0
metadata	author version scope auto_invoke prowler-cloud 1.0 root ui Writing Vitest tests Writing React component tests Writing unit tests for UI Testing hooks or utilities
allowed-tools	Read, Edit, Write, Glob, Grep, Bash, Task

For E2E tests: Use prowler-test-ui skill (Playwright). 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