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React component and hook testing patterns with Testing Library and Vitest. Use when writing tests for React components, custom hooks, or data fetching logic. Covers component rendering tests, user interaction simulation, async state testing, MSW for API mocking, hook testing with renderHook, accessibility assertions, and snapshot testing guidelines. Does NOT cover E2E tests (use e2e-testing) or TDD workflow enforcement (use tdd-workflow).
npx skill4agent add hieutrtr/ai1-skills react-testing-patternsrenderHooke2e-testingpytest-patternstdd-workflowreact-frontend-expertgetByRolegetByLabelTextgetByPlaceholderTextgetByTextgetByDisplayValuegetByAltTextgetByTestIduserEventfireEventimport userEvent from "@testing-library/user-event";
// Good — simulates real user behavior
const user = userEvent.setup();
await user.click(button);
await user.type(input, "hello");
// Bad — low-level event dispatch
fireEvent.click(button);useStateimport { render, screen } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { axe } from "jest-axe";
import { UserCard } from "./UserCard";
describe("UserCard", () => {
const defaultProps = {
user: { id: 1, displayName: "Alice", email: "alice@example.com" },
onEdit: vi.fn(),
};
it("renders user name", () => {
// Arrange
render(<UserCard {...defaultProps} />);
// Assert
expect(screen.getByText("Alice")).toBeInTheDocument();
});
it("calls onEdit when edit button is clicked", async () => {
// Arrange
const user = userEvent.setup();
render(<UserCard {...defaultProps} />);
// Act
await user.click(screen.getByRole("button", { name: /edit/i }));
// Assert
expect(defaultProps.onEdit).toHaveBeenCalledWith(1);
});
it("has no accessibility violations", async () => {
const { container } = render(<UserCard {...defaultProps} />);
expect(await axe(container)).toHaveNoViolations();
});
});it("shows user data after loading", async () => {
render(<UserProfile userId={1} />);
// Loading state
expect(screen.getByText(/loading/i)).toBeInTheDocument();
// Wait for data to appear
await waitFor(() => {
expect(screen.getByText("Alice")).toBeInTheDocument();
});
// Loading state gone
expect(screen.queryByText(/loading/i)).not.toBeInTheDocument();
});it("shows user data after loading", async () => {
render(<UserProfile userId={1} />);
// findBy = getBy + waitFor — preferred for async appearance
const heading = await screen.findByRole("heading", { name: "Alice" });
expect(heading).toBeInTheDocument();
});findBy*waitForgetBy*it("shows error message on API failure", async () => {
// Override MSW handler for this test
server.use(
http.get("/api/users/:id", () => {
return HttpResponse.json(
{ detail: "User not found" },
{ status: 404 },
);
}),
);
render(<UserProfile userId={999} />);
const error = await screen.findByRole("alert");
expect(error).toHaveTextContent(/not found/i);
});// test/mocks/handlers.ts
import { http, HttpResponse } from "msw";
export const handlers = [
http.get("/api/users", () => {
return HttpResponse.json({
items: [
{ id: 1, displayName: "Alice", email: "alice@example.com" },
{ id: 2, displayName: "Bob", email: "bob@example.com" },
],
next_cursor: null,
has_more: false,
});
}),
http.get("/api/users/:id", ({ params }) => {
return HttpResponse.json({
id: Number(params.id),
displayName: "Alice",
email: "alice@example.com",
});
}),
http.post("/api/users", async ({ request }) => {
const body = await request.json();
return HttpResponse.json(
{ id: 3, ...body, created_at: new Date().toISOString() },
{ status: 201 },
);
}),
];// test/mocks/server.ts
import { setupServer } from "msw/node";
import { handlers } from "./handlers";
export const server = setupServer(...handlers);// test/setup.ts (Vitest setup file)
import { server } from "./mocks/server";
beforeAll(() => server.listen({ onUnhandledRequest: "error" }));
afterEach(() => server.resetHandlers());
afterAll(() => server.close());server.use(
http.get("/api/users", () => {
return HttpResponse.json({ items: [], next_cursor: null, has_more: false });
}),
);import { renderHook, act } from "@testing-library/react";
import { useDebounce } from "./useDebounce";
describe("useDebounce", () => {
beforeEach(() => { vi.useFakeTimers(); });
afterEach(() => { vi.useRealTimers(); });
it("returns initial value immediately", () => {
const { result } = renderHook(() => useDebounce("hello", 300));
expect(result.current).toBe("hello");
});
it("debounces value changes", () => {
const { result, rerender } = renderHook(
({ value }) => useDebounce(value, 300),
{ initialProps: { value: "hello" } },
);
rerender({ value: "world" });
expect(result.current).toBe("hello"); // Still old value
act(() => { vi.advanceTimersByTime(300); });
expect(result.current).toBe("world"); // Now updated
});
});import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
function createWrapper() {
const queryClient = new QueryClient({
defaultOptions: { queries: { retry: false } },
});
return ({ children }) => (
<QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
);
}
it("fetches users", async () => {
const { result } = renderHook(() => useUsers(), { wrapper: createWrapper() });
await waitFor(() => expect(result.current.isSuccess).toBe(true));
expect(result.current.data).toHaveLength(2);
});import { axe, toHaveNoViolations } from "jest-axe";
expect.extend(toHaveNoViolations);
it("has no accessibility violations", async () => {
const { container } = render(<UserCard {...defaultProps} />);
const results = await axe(container);
expect(results).toHaveNoViolations();
});// test/utils.tsx
import { render, RenderOptions } from "@testing-library/react";
import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
import { MemoryRouter } from "react-router-dom";
import { AuthProvider } from "@/contexts/AuthContext";
function AllProviders({ children }: { children: React.ReactNode }) {
const queryClient = new QueryClient({
defaultOptions: { queries: { retry: false, gcTime: 0 } },
});
return (
<QueryClientProvider client={queryClient}>
<MemoryRouter>
<AuthProvider>{children}</AuthProvider>
</MemoryRouter>
</QueryClientProvider>
);
}
export function renderWithProviders(ui: React.ReactElement, options?: RenderOptions) {
return render(ui, { wrapper: AllProviders, ...options });
}describe("CreateUserForm", () => {
it("submits valid data", async () => {
const onSubmit = vi.fn();
const user = userEvent.setup();
render(<CreateUserForm onSubmit={onSubmit} />);
await user.type(screen.getByLabelText(/email/i), "test@example.com");
await user.type(screen.getByLabelText(/name/i), "Test User");
await user.click(screen.getByRole("button", { name: /create/i }));
expect(onSubmit).toHaveBeenCalledWith({
email: "test@example.com",
displayName: "Test User",
role: "member",
});
});
it("shows validation errors for empty required fields", async () => {
const user = userEvent.setup();
render(<CreateUserForm onSubmit={vi.fn()} />);
await user.click(screen.getByRole("button", { name: /create/i }));
expect(await screen.findByText(/required/i)).toBeInTheDocument();
});
});QueryClientProviderMemoryRouter<MemoryRouter initialEntries={["/users/1"]}>useParamsuseNavigatefindBy*waitForgetBy*waitForwaitFor(() => ..., { timeout: 5000 })screencontainercleanup()references/component-test-template.tsxreferences/msw-handler-examples.tsreferences/hook-test-template.tsx