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Version: 25.x

Testando Apps React

No Facebook, usamos Jest para testar aplicativos React.

Instalação#

Instalação com Create React App#

Se você é novo no React, recomendamos que use Create React App. Está pronto para uso e já vem com Jest! Você só precisa adicionar o pacote react-test-renderer para renderizar snapshots.

Execute

yarn add --dev react-test-renderer

Instalação sem Create React App#

Se você tiver uma aplicação existente vai precisar instalar alguns pacotes para que tudo funcione bem junto. Estamos usando o pacote babel-jest e o preset react do Babel para transformar nosso código dentro do ambiente de teste. Consulte também usando Babel.

Execute

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

Seu package.json deve parecer algo como isto (onde <current-version> é o número da versão mais recente para o pacote). Por favor, adicione as entradas scripts e de configuração 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'],
};

E você está pronto para ir!

Teste de Snapshot#

Vamos criar um teste de snapshot para um componente chamado Link que renderiza hiperlinks:

// Link.react.js
import React, {useState} from 'react';
const STATUS = {
HOVERED: 'hovered',
NORMAL: 'normal',
};
const 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>
);
};
export default Link;

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.

Agora vamos usar o renderer de teste do React e o recurso de snapshot do Jest para interagir com o componente e capturar a saída renderizada e criar um arquivo de snapshot:

// Link.react.test.js
import React from 'react';
import renderer from 'react-test-renderer';
import Link from '../Link.react';
test('Link 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
tree.props.onMouseEnter();
// re-rendering
tree = component.toJSON();
expect(tree).toMatchSnapshot();
// manually trigger the callback
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.react.test.js.snap
exports[`Link changes the class when hovered 1`] = `
<a
className="normal"
href="http://www.facebook.com"
onMouseEnter={[Function]}
onMouseLeave={[Function]}>
Facebook
</a>
`;
exports[`Link changes the class when hovered 2`] = `
<a
className="hovered"
href="http://www.facebook.com"
onMouseEnter={[Function]}
onMouseLeave={[Function]}>
Facebook
</a>
`;
exports[`Link changes the class when hovered 3`] = `
<a
className="normal"
href="http://www.facebook.com"
onMouseEnter={[Function]}
onMouseLeave={[Function]}>
Facebook
</a>
`;

Da próxima vez que você executar os testes, a saída renderizada será comparada ao snapshot criado anteriormente. The snapshot should be committed along with code changes. Quando um teste de snapshot falhar, você precisa inspecionar se é uma mudança pretendida ou não intencional. Se a mudança é esperada, você pode invocar Jest com jest -u para substituir o snapshot existente.

O código pra esse exemplo está disponível em examples/snapshot.

Teste de Snapshot com Mocks, Enzyme e 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: js jest.mock('./SomeComponent', () => () => 'SomeComponent');
    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.
    tsx
    jest.mock('./Widget', () =&#062; () =&#062; <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'));
    Disable warnings all together (should be done in your jest setup file): js 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.

Testando o DOM#

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

react-testing-library#

You have to run yarn add --dev @testing-library/react to use react-testing-library.

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

// CheckboxWithLabel.js
import React, {useState} from 'react';
const 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>
);
};
export default CheckboxWithLabel;
// __tests__/CheckboxWithLabel-test.js
import React from 'react';
import {cleanup, fireEvent, render} from '@testing-library/react';
import CheckboxWithLabel from '../CheckboxWithLabel';
// Note: running cleanup afterEach is done automatically for you in @testing-library/[email protected] 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.

Enzyme#

You have to run yarn add --dev enzyme to use Enzyme. If you are using a React version below 15.5.0, you will also need to install react-addons-test-utils.

Let's rewrite the test from above using Enzyme instead of react-testing-library. Nós usamos o renderizador superficial do Enzyme neste exemplo.

// __tests__/CheckboxWithLabel-test.js
import React from 'react';
import {shallow} from 'enzyme';
import CheckboxWithLabel from '../CheckboxWithLabel';
test('CheckboxWithLabel changes the text after click', () => {
// Render a checkbox with label in the document
const checkbox = shallow(<CheckboxWithLabel labelOn="On" labelOff="Off" />);
expect(checkbox.text()).toEqual('Off');
checkbox.find('input').simulate('change');
expect(checkbox.text()).toEqual('On');
});

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

Transformadores personalizados#

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.

Para fazer isto funcionar com Jest você precisa atualizar sua configuração Jest com isso: "transform": {"\\.js$": "path/to/custom-transformer.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'],
});