React Testing Library is ignoring media query in styled component

React Testing Library is designed to test your components in a similar way to how a user would interact with them. When it comes to media queries and styled components, it's important to consider that React Testing Library renders components in a virtual DOM, and it does not execute real CSS media queries during testing. As a result, the media query styles won't be applied automatically when using React Testing Library.

To properly test components with media queries and styled components, you have a few options:

1. Mocking Window Dimensions: One way to test media queries is by manually mocking the window dimensions. You can do this by using the @testing-library/react-hooks package to mock the window.innerWidth and window.innerHeight values to simulate different screen sizes. This can be useful if you want to test how your components respond to different screen sizes.

2. Test Different States: Instead of testing media queries directly, consider testing different states of your components based on the expected behavior at different screen sizes. For example, you can test how your component renders with certain props or state values that trigger different styles or layout changes.

3. Integration Testing: Integration testing with real browsers, such as using tools like Cypress or Puppeteer, allows you to test your components in an environment closer to the real browser behavior. These tools can evaluate media queries and apply styles based on the actual window size.

Here's an example of how you can manually mock the window dimensions using @testing-library/react-hooks:

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npm install @testing-library/react-hooks

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// myComponent.test.js
import React from 'react';
import { render } from '@testing-library/react';
import { useWindowSize } from '@testing-library/react-hooks';
import MyComponent from './MyComponent';

jest.mock('@testing-library/react-hooks', () => ({
  ...jest.requireActual('@testing-library/react-hooks'),
  useWindowSize: jest.fn(),
}));

describe('MyComponent', () => {
  it('renders correctly at different screen sizes', () => {
    // Mock different screen sizes
    useWindowSize.mockReturnValue({ width: 375, height: 667 }); // e.g., iPhone 6/7/8 screen size

    const { getByTestId } = render(<MyComponent />);
    // Test the expected behavior of your component based on the mocked screen size

    useWindowSize.mockReturnValue({ width: 1440, height: 900 }); // e.g., desktop screen size

    const { getByTestId } = render(<MyComponent />);
    // Test the expected behavior of your component based on the mocked screen size
  });
});

Keep in mind that manually mocking window dimensions might not cover all scenarios perfectly, and it's essential to consider the trade-offs between different testing strategies. Integration testing with real browsers is usually the most accurate way to test media queries and styled components, but it comes with its own setup and maintenance complexities.