Itechmeat LLM Code React Testing Library

React Testing Library Skill

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Installation

Install: npm install --save-dev @testing-library/react @testing-library/dom. Recommended extras: @testing-library/user-event and @testing-library/jest-dom. React 19 requires v16.1.0+.

Core Philosophy

"The more your tests resemble the way your software is used, the more confidence they can give you."

Avoid testing:

• Internal state of components
• Internal methods
• Lifecycle methods
• Child component implementation details

Test instead:

• What users see and interact with
• Behavior from user's perspective
• Accessibility (queries by role, label)

Query Priority

Use queries in this order of preference:

1. Accessible to Everyone (Preferred)

// Best — by ARIA role
getByRole("button", { name: /submit/i });
getByRole("textbox", { name: /email/i });

// Form fields — by label
getByLabelText("Email");

// Non-interactive content — by text
getByText("Welcome back!");

2. Semantic Queries

// Images
getByAltText("Company logo");

// Title attribute (less reliable)
getByTitle("Close");

3. Test IDs (Escape Hatch)

// Only when other queries don't work
getByTestId("custom-element");

Query Types

When to use:

• getBy* — element exists
• queryBy* — element may not exist (assertions like expect(...).not.toBeInTheDocument())
• findBy* — element appears asynchronously

Basic Test Pattern

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

test("shows greeting after login", async () => {
  const user = userEvent.setup();
  render(<App />);

  // Act — simulate user interactions
  await user.type(screen.getByLabelText(/username/i), "john");
  await user.click(screen.getByRole("button", { name: /login/i }));

  // Assert — verify outcome
  expect(await screen.findByText(/welcome, john/i)).toBeInTheDocument();
});

User Events

Always use @testing-library/user-event over fireEvent:

import userEvent from "@testing-library/user-event";

test("user interactions", async () => {
  const user = userEvent.setup();

  // Click
  await user.click(element);
  await user.dblClick(element);
  await user.tripleClick(element);

  // Type
  await user.type(input, "Hello");
  await user.clear(input);

  // Select
  await user.selectOptions(select, ["option1", "option2"]);

  // Keyboard
  await user.keyboard("{Enter}");
  await user.keyboard("[ShiftLeft>]a[/ShiftLeft]"); // Shift+A

  // Clipboard
  await user.copy();
  await user.paste();

  // Pointer
  await user.hover(element);
  await user.unhover(element);
});

Async Patterns

waitFor — Retry Until Success

await waitFor(() => {
  expect(screen.getByText("Loaded")).toBeInTheDocument();
});

// With options
await waitFor(() => expect(callback).toHaveBeenCalled(), {
  timeout: 5000,
  interval: 100,
});

findBy — Built-in waitFor

// Equivalent to: await waitFor(() => getByText('Loaded'))
const element = await screen.findByText("Loaded");

waitForElementToBeRemoved

await waitForElementToBeRemoved(() => screen.queryByText("Loading..."));

Common Patterns

Custom Render with Providers

// test-utils.tsx
import { render } from "@testing-library/react";
import { ThemeProvider } from "./ThemeProvider";
import { AuthProvider } from "./AuthProvider";

function AllProviders({ children }) {
  return (
    <ThemeProvider>
      <AuthProvider>{children}</AuthProvider>
    </ThemeProvider>
  );
}

const customRender = (ui, options) => render(ui, { wrapper: AllProviders, ...options });

export * from "@testing-library/react";
export { customRender as render };

Testing Hooks

import { renderHook, act } from "@testing-library/react";

test("useCounter increments", () => {
  const { result } = renderHook(() => useCounter());

  expect(result.current.count).toBe(0);

  act(() => {
    result.current.increment();
  });

  expect(result.current.count).toBe(1);
});

Rerender with New Props

const { rerender } = render(<Counter count={1} />);
expect(screen.getByText("Count: 1")).toBeInTheDocument();

rerender(<Counter count={2} />);
expect(screen.getByText("Count: 2")).toBeInTheDocument();

Query Within Container

import { within } from "@testing-library/react";

const modal = screen.getByRole("dialog");
const submitBtn = within(modal).getByRole("button", { name: /submit/i });

Debugging

// Print entire DOM
screen.debug();

// Print specific element
screen.debug(screen.getByRole("button"));

// Log available roles
import { logRoles } from "@testing-library/react";
logRoles(container);

// With prettyDOM options
screen.debug(undefined, 10000); // max length

jest-dom Matchers

import "@testing-library/jest-dom";

expect(element).toBeInTheDocument();
expect(element).toBeVisible();
expect(element).toBeEnabled();
expect(element).toBeDisabled();
expect(element).toHaveTextContent("Hello");
expect(element).toHaveValue("input value");
expect(element).toHaveAttribute("href", "/home");
expect(element).toHaveClass("active");
expect(element).toHaveFocus();
expect(element).toBeChecked();

Configuration

import { configure } from "@testing-library/react";

configure({
  // Custom test ID attribute
  testIdAttribute: "data-my-test-id",

  // Async timeout
  asyncUtilTimeout: 5000,

  // Default hidden
  defaultHidden: true,

  // Throw suggestions (debugging)
  throwSuggestions: true,
});

❌ Prohibitions (Anti-patterns)

// ❌ Don't query by class/id
container.querySelector(".my-class");

// ❌ Don't use container.firstChild
const { container } = render(<Component />);
expect(container.firstChild).toHaveClass("active");

// ❌ Don't use fireEvent when userEvent works
fireEvent.click(button); // Use userEvent.click instead

// ❌ Don't test implementation details
expect(component.state.loading).toBe(false);

// ❌ Don't use waitFor with findBy
await waitFor(() => screen.findByText("x")); // findBy already waits

// ❌ Don't assert inside waitFor callback (unless necessary)
await waitFor(() => {
  expect(mockFn).toHaveBeenCalled(); // OK - need to wait for call
});

✅ Best Practices

// ✅ Use screen for all queries
import { render, screen } from "@testing-library/react";
render(<Component />);
screen.getByRole("button"); // Good

// ✅ Prefer userEvent over fireEvent
const user = userEvent.setup();
await user.click(button);

// ✅ Use findBy for async elements
const element = await screen.findByText("Loaded");

// ✅ Use queryBy for non-existence assertions
expect(screen.queryByText("Error")).not.toBeInTheDocument();

// ✅ Use within for scoped queries
const form = screen.getByRole("form");
within(form).getByLabelText("Email");

// ✅ Use accessible queries (role, label, text)
getByRole("button", { name: /submit/i });

TextMatch Options

// Exact match (default)
getByText("Hello World");

// Substring match
getByText("llo Worl", { exact: false });

// Regex
getByText(/hello world/i);

// Custom function
getByText((content, element) => {
  return element.tagName === "SPAN" && content.startsWith("Hello");
});

Quick Reference

Links

• Documentation
• Releases
• GitHub
• npm

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