React Testing Library: מדריך מקיף

            npm install --save-dev @testing-library/react @testing-library/jest-dom jest babel-jest @babel/preset-env @babel/preset-react

            

              
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            yarn add --dev @testing-library/react @testing-library/jest-dom jest babel-jest @babel/preset-env @babel/preset-react

            

              
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            module.exports = {
  presets: ['@babel/preset-env', '@babel/preset-react'],
};

            

              
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            {
  "scripts": {
    "test": "jest"
  }
}

            

              
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            module.exports = {
  testEnvironment: 'jsdom',
  setupFilesAfterEnv: ['/src/setupTests.js'],
};

            

              
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            import '@testing-library/jest-dom/extend-expect';

            

              
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            // src/components/Greeting.js
import React from 'react';

function Greeting({ name }) {
  return <h1>Hello, {name}!</h1>;
}

export default Greeting;

            

              
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            // src/components/Greeting.test.js
import React from 'react';
import { render, screen } from '@testing-library/react';
import Greeting from './Greeting';

test('renders a greeting message', () => {
  render(<Greeting name="World" />);
  const greetingElement = screen.getByText(/Hello, World!/i);
  expect(greetingElement).toBeInTheDocument();
});

            

              
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            npm test

            

              
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            <button role="button">Click me</button>

            

              
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            const buttonElement = screen.getByRole('button');
expect(buttonElement).toBeInTheDocument();

            

              
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            <label htmlFor="name">Name:</label>
<input type="text" id="name" />

            

              
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            const nameInputElement = screen.getByLabelText('Name:');
expect(nameInputElement).toBeInTheDocument();

            

              
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            <input type="text" placeholder="Enter your email" />

            

              
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            const emailInputElement = screen.getByPlaceholderText('Enter your email');
expect(emailInputElement).toBeInTheDocument();

            

              
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            <img src="logo.png" alt="Company Logo" />

            

              
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            const logoImageElement = screen.getByAltText('Company Logo');
expect(logoImageElement).toBeInTheDocument();

            

              
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            <span title="Close">X</span>

            

              
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            const closeElement = screen.getByTitle('Close');
expect(closeElement).toBeInTheDocument();

            

              
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            <input type="text" value="Initial Value" />

            

              
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            const inputElement = screen.getByDisplayValue('Initial Value');
expect(inputElement).toBeInTheDocument();

            

              
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            <li>Item 1</li>
<li>Item 2</li>
<li>Item 3</li>

            

              
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            const listItems = screen.getAllByRole('listitem');
expect(listItems).toHaveLength(3);

            

              
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            const missingElement = screen.queryByText('Non-existent text');
expect(missingElement).toBeNull();

            

              
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            // Simulating an asynchronous data fetch
const fetchData = () => new Promise(resolve => {
  setTimeout(() => resolve('Data Loaded!'), 1000);
});

function MyComponent() {
  const [data, setData] = React.useState(null);

  React.useEffect(() => {
    fetchData().then(setData);
  }, []);

  return <div>{data}</div>;
}

            

              
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            test('loads data asynchronously', async () => {
  render(<MyComponent />);
  const dataElement = await screen.findByText('Data Loaded!');
  expect(dataElement).toBeInTheDocument();
});

            

              
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            <button onClick={() => alert('Button clicked!')}>Click me</button>

            

              
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            import { fireEvent } from '@testing-library/react';

test('simulates a button click', () => {
  const alertMock = jest.spyOn(window, 'alert').mockImplementation(() => {});
  render(<button onClick={() => alert('Button clicked!')}>Click me</button>);
  const buttonElement = screen.getByRole('button');
  fireEvent.click(buttonElement);
  expect(alertMock).toHaveBeenCalledTimes(1);
  alertMock.mockRestore();
});

            

              
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            <input type="text" onChange={e => console.log(e.target.value)} />

            

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

test('simulates typing in an input field', () => {
  const inputElement = screen.getByRole('textbox');
  userEvent.type(inputElement, 'Hello, world!');
  expect(inputElement).toHaveValue('Hello, world!');
});

            

              
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            function MyComponent() {
  const [data, setData] = React.useState(null);

  React.useEffect(() => {
    setTimeout(() => {
      setData('Data loaded!');
    }, 1000);
  }, []);

  return <div>{data}</div>;
}

            

              
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            import { waitFor } from '@testing-library/react';

test('waits for data to load', async () => {
  render(<MyComponent />);
  await waitFor(() => screen.getByText('Data loaded!'));
  const dataElement = screen.getByText('Data loaded!');
  expect(dataElement).toBeInTheDocument();
});

            

              
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            // src/hooks/useCounter.js
import { useState } from 'react';

function useCounter(initialValue = 0) {
  const [count, setCount] = useState(initialValue);

  const increment = () => {
    setCount(prevCount => prevCount + 1);
  };

  const decrement = () => {
    setCount(prevCount => prevCount - 1);
  };

  return { count, increment, decrement };
}

export default useCounter;

            

              
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            // src/hooks/useCounter.test.js
import { renderHook, act } from '@testing-library/react';
import useCounter from './useCounter';

test('increments the counter', () => {
  const { result } = renderHook(() => useCounter());

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

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

            

              
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            // src/api/dataService.js
export const fetchData = async () => {
  const response = await fetch('/api/data');
  const data = await response.json();
  return data;
};

            

              
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            // src/components/MyComponent.js
import React, { useState, useEffect } from 'react';
import { fetchData } from '../api/dataService';

function MyComponent() {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetchData().then(setData);
  }, []);

  return <div>{data}</div>;
}

            

              
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            // src/components/MyComponent.test.js
import { render, screen, waitFor } from '@testing-library/react';
import MyComponent from './MyComponent';
import * as dataService from '../api/dataService';

jest.mock('../api/dataService');

test('fetches data from the API', async () => {
  dataService.fetchData.mockResolvedValue({ message: 'Mocked data!' });

  render(<MyComponent />);

  await waitFor(() => screen.getByText('Mocked data!'));

  expect(screen.getByText('Mocked data!')).toBeInTheDocument();
  expect(dataService.fetchData).toHaveBeenCalledTimes(1);
});

            

              
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            // src/contexts/ThemeContext.js
import React, { createContext, useState } from 'react';

export const ThemeContext = createContext();

export function ThemeProvider({ children }) {
  const [theme, setTheme] = useState('light');

  const toggleTheme = () => {
    setTheme(prevTheme => (prevTheme === 'light' ? 'dark' : 'light'));
  };

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  );
}

            

              
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            // src/components/MyComponent.js
import React, { useContext } from 'react';
import { ThemeContext } from '../contexts/ThemeContext';

function MyComponent() {
  const { theme, toggleTheme } = useContext(ThemeContext);

  return (
    <div style={{ backgroundColor: theme === 'light' ? '#fff' : '#000', color: theme === 'light' ? '#000' : '#fff' }}>
      <p>Current theme: {theme}</p>
      <button onClick={toggleTheme}>Toggle Theme</button>
    </div>
  );
}

            

              
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            // src/components/MyComponent.test.js
import { render, screen, fireEvent } from '@testing-library/react';
import MyComponent from './MyComponent';
import { ThemeProvider } from '../contexts/ThemeContext';

test('toggles the theme', () => {
  render(
    <ThemeProvider>
      <MyComponent />
    </ThemeProvider>
  );

  const themeParagraph = screen.getByText(/Current theme: light/i);
  const toggleButton = screen.getByRole('button', { name: /Toggle Theme/i });

  expect(themeParagraph).toBeInTheDocument();

  fireEvent.click(toggleButton);

  expect(screen.getByText(/Current theme: dark/i)).toBeInTheDocument();
});

            

              
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            // src/components/MyComponent.js
import React from 'react';
import { Link } from 'react-router-dom';

function MyComponent() {
  return (
    <div>
      <Link to="/about">Go to About Page</Link>
    </div>
  );
}

            

              
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            // src/components/MyComponent.test.js
import { render, screen } from '@testing-library/react';
import { MemoryRouter } from 'react-router-dom';
import MyComponent from './MyComponent';

test('renders a link to the about page', () => {
  render(
    <MemoryRouter>
      <MyComponent />
    </MemoryRouter>
  );

  const linkElement = screen.getByRole('link', { name: /Go to About Page/i });
  expect(linkElement).toBeInTheDocument();
  expect(linkElement).toHaveAttribute('href', '/about');
});

            

              
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