Testing Library

When to Use

• Testing UI components with @testing-library/react, @testing-library/vue, or

@testing-library/dom.

• Choosing the right query method for elements.
• Simulating user interactions (typing, clicking, selecting).
• Testing async behavior (data fetching, loading states, debounced input).
• Writing tests that enforce and verify accessibility.

Critical Patterns

• Test User Behavior, Not Implementation: Your tests should resemble how users interact with

your app. Query by role, label, and text — not by class, test ID, or component internals.

• Query Priority: Follow this order strictly — it maps to accessibility:

1. getByRole — accessible roles (button, textbox, heading)
2. getByLabelText — form fields with labels
3. getByPlaceholderText — when no label exists
4. getByText — visible text content
5. getByDisplayValue — current input values
6. getByAltText — images
7. getByTitle — title attribute
8. getByTestId — LAST RESORT only

• userEvent Over fireEvent: Always use @testing-library/user-event for interactions. It

simulates real browser behavior (focus, keydown, keyup, input) while fireEvent dispatches a single synthetic event.

• No Implementation Details: NEVER assert on component state, props, or internal methods. NEVER

query by class name or component structure.

• Async by Default: Use findBy queries (which return Promises) or wrap assertions in waitFor

for any UI that updates asynchronously.

Code Examples

Query Priority in Practice

import { render, screen } from "@testing-library/react";
import { SignupForm } from "./SignupForm";

it("renders the signup form with accessible elements", () => {
  render();

  // BEST — getByRole with accessible name
  screen.getByRole("heading", { name: /create account/i });
  screen.getByRole("textbox", { name: /email/i });
  screen.getByRole("button", { name: /sign up/i });

  // GOOD — getByLabelText for form fields
  screen.getByLabelText(/password/i);

  // ACCEPTABLE — getByText for static content
  screen.getByText(/already have an account/i);

  // LAST RESORT — only when element has no accessible role or text
  screen.getByTestId("captcha-widget");
});

User Events — The Right Way

import { render, screen } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { SearchBar } from "./SearchBar";

describe("SearchBar", () => {
  it("calls onSearch when user types and submits", async () => {
    const user = userEvent.setup(); // Always call setup() first
    const onSearch = jest.fn();
    render();

    const input = screen.getByRole("searchbox", { name: /search/i });

    await user.type(input, "testing library");
    await user.keyboard("{Enter}");

    expect(onSearch).toHaveBeenCalledWith("testing library");
  });

  it("clears input when clear button is clicked", async () => {
    const user = userEvent.setup();
    render();

    const input = screen.getByRole("searchbox", { name: /search/i });
    await user.type(input, "some query");
    expect(input).toHaveValue("some query");

    await user.click(screen.getByRole("button", { name: /clear/i }));
    expect(input).toHaveValue("");
  });
});

Async Testing Patterns

import { render, screen, waitFor } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { UserProfile } from "./UserProfile";

it("loads and displays user data", async () => {
  render();

  // findBy queries wait for the element to appear (default timeout: 1000ms)
  const heading = await screen.findByRole("heading", { name: /alice/i });
  expect(heading).toBeInTheDocument();
});

it("shows error state when fetch fails", async () => {
  server.use(
    rest.get("/api/users/1", (_req, res, ctx) =>
      res(ctx.status(500))
    )
  );

  render();

  // waitFor retries the assertion until it passes
  await waitFor(() => {
    expect(screen.getByRole("alert")).toHaveTextContent(/failed to load/i);
  });
});

it("shows loading then content", async () => {
  render();

  // Loading state appears first
  expect(screen.getByText(/loading/i)).toBeInTheDocument();

  // Content replaces loading
  await waitFor(() => {
    expect(screen.queryByText(/loading/i)).not.toBeInTheDocument();
  });
  expect(screen.getByRole("heading", { name: /alice/i })).toBeInTheDocument();
});

Testing Forms

import { render, screen } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { ContactForm } from "./ContactForm";

describe("ContactForm", () => {
  it("submits form with valid data", async () => {
    const user = userEvent.setup();
    const onSubmit = jest.fn();
    render();

    await user.type(screen.getByLabelText(/name/i), "Alice");
    await user.type(screen.getByLabelText(/email/i), "alice@example.com");

    // Select from dropdown — use selectOptions
    await user.selectOptions(
      screen.getByRole("combobox", { name: /topic/i }),
      "support"
    );

    // Checkbox
    await user.click(screen.getByRole("checkbox", { name: /agree to terms/i }));

    await user.click(screen.getByRole("button", { name: /submit/i }));

    expect(onSubmit).toHaveBeenCalledWith({
      name: "Alice",
      email: "alice@example.com",
      topic: "support",
      agreedToTerms: true,
    });
  });

  it("displays validation errors for empty required fields", async () => {
    const user = userEvent.setup();
    render();

    await user.click(screen.getByRole("button", { name: /submit/i }));

    expect(screen.getByText(/name is required/i)).toBeInTheDocument();
    expect(screen.getByText(/email is required/i)).toBeInTheDocument();
  });
});

Testing Modals and Portals

import { render, screen, within } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { ConfirmDialog } from "./ConfirmDialog";

it("opens and confirms deletion", async () => {
  const user = userEvent.setup();
  const onConfirm = jest.fn();
  render();

  // Open dialog
  await user.click(screen.getByRole("button", { name: /delete item/i }));

  // Scope assertions to the dialog
  const dialog = screen.getByRole("dialog");
  expect(within(dialog).getByText(/are you sure/i)).toBeInTheDocument();

  // Confirm
  await user.click(within(dialog).getByRole("button", { name: /confirm/i }));

  expect(onConfirm).toHaveBeenCalledTimes(1);
  expect(screen.queryByRole("dialog")).not.toBeInTheDocument();
});

Accessibility Assertions

import { render } from "@testing-library/react";
import { axe, toHaveNoViolations } from "jest-axe";
import { Navigation } from "./Navigation";

expect.extend(toHaveNoViolations);

it("has no accessibility violations", async () => {
  const { container } = render();
  const results = await axe(container);
  expect(results).toHaveNoViolations();
});

Custom Render with Providers

// test-utils.tsx
import { render, RenderOptions } from "@testing-library/react";
import { ThemeProvider } from "./ThemeProvider";
import { QueryClient, QueryClientProvider } from "@tanstack/react-query";

function AllProviders({ children }: { children: React.ReactNode }) {
  const queryClient = new QueryClient({
    defaultOptions: { queries: { retry: false } },
  });

  return (
    
      {children}
    
  );
}

export function renderWithProviders(
  ui: React.ReactElement,
  options?: Omit,
) {
  return render(ui, { wrapper: AllProviders, ...options });
}

// Re-export everything from testing-library
export * from "@testing-library/react";
export { renderWithProviders as render };

Best Practices

DO

• Use screen for all queries — it's always scoped to document.body and requires no

destructuring.

• Use within() to scope queries to a specific container (dialog, list item, section).
• Use getByRole as your default query — it verifies accessibility and finds elements reliably.
• Use regex with case-insensitive flag (/submit/i) for text matching — it's resilient to casing

changes.

• Create a custom render function that includes your app's providers (theme, router, query

client).

• Use MSW (Mock Service Worker) for API mocking — it works at the network level and shares mocks

between tests and development.

DON'T

• DON'T use container.querySelector(".my-class") — it tests implementation details, not user

behavior.

• DON'T use fireEvent when userEvent is available — fireEvent doesn't simulate real browser

behavior.

• DON'T use getByTestId as your first choice — it means the element lacks proper accessible roles

or labels. Fix the component first.

• DON'T assert on component state or hooks directly — test what the user sees and interacts with.
• DON'T use act() manually in most cases — userEvent and findBy handle it internally.
• DON'T use waitFor with getBy inside — use findBy instead, which is getBy + waitFor

combined.

• DON'T wrap non-async operations in waitFor — it adds unnecessary complexity and hides

synchronous bugs.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: dallay
• Source: dallay/agents-skills
• License: MIT

Install and usage instructions live in the source repository linked above.