Testarea aplicațiilor React

At Facebook, we use Jest to test React applications.

Instalare

Instalare cu Create React App

If you are new to React, we recommend using Create React App. Este gata pentru utilizare şi este livrat cu Jest! You will only need to add react-test-renderer for rendering snapshots.

Rulare

npm

npm install --save-dev react-test-renderer

Yarn

yarn add --dev react-test-renderer

pnpm

pnpm add --save-dev react-test-renderer

Instalare fără Create React App

Dacă aveţi o aplicaţie existentă trebuie să instalaţi câteva pachete pentru a face totul să funcționeze bine împreună. Noi folosim pachetul babel-jest şi presetarea babel react pentru a transforma codul nostru în mediul de testare. De asemenea, consultaţi utilizarea babel.

Rulare

npm

npm install --save-dev jest babel-jest @babel/preset-env @babel/preset-react react-test-renderer

Yarn

yarn add --dev jest babel-jest @babel/preset-env @babel/preset-react react-test-renderer

pnpm

pnpm add --save-dev jest babel-jest @babel/preset-env @babel/preset-react react-test-renderer

Fișierul package.json ar trebui să arate în felul următor (unde <current-version> este numărul real al celei mai recente versiuni pentru pachetul respectiv). Vă rugăm să adăugaţi script-uri şi configurările pentru jest:

{
  "dependencies": {
    "react": "<current-version>",
    "react-dom": "<current-version>"
  },
  "devDependencies": {
    "@babel/preset-env": "<current-version>",
    "@babel/preset-react": "<current-version>",
    "babel-jest": "<current-version>",
    "jest": "<current-version>",
    "react-test-renderer": "<current-version>"
  },
  "scripts": {
    "test": "jest"
  }
}

babel.config.js

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

Și sunteți gata de drum!

Testarea de imagine

Haideți să creăm un test de imagine pentru o componentă Link care randează hyperlink-uri:

Link.js

import {useState} from 'react';

const STATUS = {
  HOVERED: 'hovered',
  NORMAL: 'normal',
};

export default function Link({page, children}) {
  const [status, setStatus] = useState(STATUS.NORMAL);

  const onMouseEnter = () => {
    setStatus(STATUS.HOVERED);
  };

  const onMouseLeave = () => {
    setStatus(STATUS.NORMAL);
  };

  return (
    <a
      className={status}
      href={page || '#'}
      onMouseEnter={onMouseEnter}
      onMouseLeave={onMouseLeave}
    >
      {children}
    </a>
  );
}

note

Examples are using Function components, but Class components can be tested in the same way. See React: Function and Class Components. Reminders that with Class components, we expect Jest to be used to test props and not methods directly.

Acum haideţi să utilizăm procesorul de randare React şi funcționalitatea din Jest pentru testarea de imagine pentru a interacţiona cu componenta şi a captura rezultatul şi a crea un fişier de imagine:

Link.test.js

import renderer from 'react-test-renderer';
import Link from '../Link';

it('changes the class when hovered', () => {
  const component = renderer.create(
    <Link page="http://www.facebook.com">Facebook</Link>,
  );
  let tree = component.toJSON();
  expect(tree).toMatchSnapshot();

  // manually trigger the callback
  renderer.act(() => {
    tree.props.onMouseEnter();
  });
  // re-rendering
  tree = component.toJSON();
  expect(tree).toMatchSnapshot();

  // manually trigger the callback
  renderer.act(() => {
    tree.props.onMouseLeave();
  });
  // re-rendering
  tree = component.toJSON();
  expect(tree).toMatchSnapshot();
});

When you run yarn test or jest, this will produce an output file like this:

__tests__/__snapshots__/Link.test.js.snap

exports[`changes the class when hovered 1`] = `
<a
  className="normal"
  href="http://www.facebook.com"
  onMouseEnter={[Function]}
  onMouseLeave={[Function]}
>
  Facebook
</a>
`;

exports[`changes the class when hovered 2`] = `
<a
  className="hovered"
  href="http://www.facebook.com"
  onMouseEnter={[Function]}
  onMouseLeave={[Function]}
>
  Facebook
</a>
`;

exports[`changes the class when hovered 3`] = `
<a
  className="normal"
  href="http://www.facebook.com"
  onMouseEnter={[Function]}
  onMouseLeave={[Function]}
>
  Facebook
</a>
`;

Data viitoare când executaţi testele, rezultatul va fi comparat cu imaginea creată anterior. The snapshot should be committed along with code changes. Atunci când un test de imagine eșuează, trebuie să inspectați dacă este vorba de o modificare intenționată sau neintenţionată. În cazul în care schimbarea este intenționată se poate apela Jest cu jest -u pentru a suprascrie imaginea existentă.

The code for this example is available at examples/snapshot.

Snapshot Testing with Mocks, Enzyme and React 16+

There's a caveat around snapshot testing when using Enzyme and React 16+. If you mock out a module using the following style:

jest.mock('../SomeDirectory/SomeComponent', () => 'SomeComponent');

Then you will see warnings in the console:

Warning: <SomeComponent /> is using uppercase HTML. Always use lowercase HTML tags in React.

# Or:
Warning: The tag <SomeComponent> is unrecognized in this browser. If you meant to render a React component, start its name with an uppercase letter.

React 16 triggers these warnings due to how it checks element types, and the mocked module fails these checks. Your options are:

1. Render as text. This way you won't see the props passed to the mock component in the snapshot, but it's straightforward:

   jest.mock('./SomeComponent', () => () => 'SomeComponent');
2. Render as a custom element. DOM "custom elements" aren't checked for anything and shouldn't fire warnings. They are lowercase and have a dash in the name.

   jest.mock('./Widget', () => () => <mock-widget />);
3. Use react-test-renderer. The test renderer doesn't care about element types and will happily accept e.g. SomeComponent. You could check snapshots using the test renderer, and check component behavior separately using Enzyme.
4. Disable warnings all together (should be done in your jest setup file):

   jest.mock('fbjs/lib/warning', () => require('fbjs/lib/emptyFunction'));
   This shouldn't normally be your option of choice as useful warnings could be lost. However, in some cases, for example when testing react-native's components we are rendering react-native tags into the DOM and many warnings are irrelevant. Another option is to swizzle the console.warn and suppress specific warnings.

Testarea DOM

If you'd like to assert, and manipulate your rendered components you can use @testing-library/react, Enzyme, or React's TestUtils. The following example use @testing-library/react.

@testing-library/react

npm

npm install --save-dev @testing-library/react

Yarn

yarn add --dev @testing-library/react

pnpm

pnpm add --save-dev @testing-library/react

Let's implement a checkbox which swaps between two labels:

CheckboxWithLabel.js

import {useState} from 'react';

export default function CheckboxWithLabel({labelOn, labelOff}) {
  const [isChecked, setIsChecked] = useState(false);

  const onChange = () => {
    setIsChecked(!isChecked);
  };

  return (
    <label>
      <input type="checkbox" checked={isChecked} onChange={onChange} />
      {isChecked ? labelOn : labelOff}
    </label>
  );
}

__tests__/CheckboxWithLabel-test.js

import {cleanup, fireEvent, render} from '@testing-library/react';
import CheckboxWithLabel from '../CheckboxWithLabel';

// Note: running cleanup afterEach is done automatically for you in @testing-library/react@9.0.0 or higher
// unmount and cleanup DOM after the test is finished.
afterEach(cleanup);

it('CheckboxWithLabel changes the text after click', () => {
  const {queryByLabelText, getByLabelText} = render(
    <CheckboxWithLabel labelOn="On" labelOff="Off" />,
  );

  expect(queryByLabelText(/off/i)).toBeTruthy();

  fireEvent.click(getByLabelText(/off/i));

  expect(queryByLabelText(/on/i)).toBeTruthy();
});

The code for this example is available at examples/react-testing-library.

Transformatoare personalizate

If you need more advanced functionality, you can also build your own transformer. Instead of using babel-jest, here is an example of using @babel/core:

custom-transformer.js

'use strict';

const {transform} = require('@babel/core');
const jestPreset = require('babel-preset-jest');

module.exports = {
  process(src, filename) {
    const result = transform(src, {
      filename,
      presets: [jestPreset],
    });

    return result || src;
  },
};

Don't forget to install the @babel/core and babel-preset-jest packages for this example to work.

Pentru a face acest lucru cu Jest trebuie să actualizați configurația Jest cu: "transform": {"\\.js$": "calea/catre/transformatorul-personalizat.js"}.

If you'd like to build a transformer with babel support, you can also use babel-jest to compose one and pass in your custom configuration options:

const babelJest = require('babel-jest');

module.exports = babelJest.createTransformer({
  presets: ['my-custom-preset'],
});

See dedicated docs for more details.