Simple React Native testing utilities helping you write better tests with less effort
Appreciation notice: This project is heavily inspired by react-testing-library. Go check it out and use it to test your web React apps.
You want to write maintainable tests for your React Native components without testing implementation details, but then you're told to use Enzyme, which you learn has no React Native adapter, meaning only shallow rendering is supported. And you want to render deep! But deep rendering may otherwise require jsdom (React Native isn't the web!), while doing deep rendering with react-test-renderer is so painful.
You would also like to use the newest React features, but you need to wait for your testing library's abstractions to catch up and it takes a while.
You finally want to approach testing using only best practices, while Enzyme may encourage assertions on implementation details.
The react-native-testing-library is a lightweight solution for testing your React Native components. It provides light utility functions on top of react-test-renderer letting you always be up to date with latest React features and write any component tests you like, be it shallow or deeply rendered ones. But really not any, it prevents you from testing implementation details because we stand this is a very bad practice.
This library is a replacement for Enzyme.
import { render, fireEvent } from 'react-native-testing-library';
import { QuestionsBoard } from '../QuestionsBoard';
function setAnswer(question, answer) {
fireEvent.changeText(question, answer);
}
test('should verify two questions', () => {
const { getAllByName, getByText } = render(<QuestionsBoard {...props} />);
const allQuestions = getAllByName('Question');
setAnswer(allQuestions[0], 'a1');
setAnswer(allQuestions[1], 'a2');
fireEvent.press(getByText('submit'));
expect(props.verifyQuestions).toBeCalledWith({
'1': { q: 'q1', a: 'a1' },
'2': { q: 'q2', a: 'a2' },
});
});Open a Terminal in your project's folder and run:
yarn add --dev react-native-testing-libraryThis library has a peerDependencies listing for react-test-renderer and, of course, react. Make sure to install them too!
As you may have noticed, it's not tied to React Native at all – you can safely use it in your React components if you feel like not interacting directly with DOM.
Defined as:
function render(
component: React.Element<*>,
options?: {
/* You won't often use this, but it's helpful when testing refs */
createNodeMock: (element: React.Element<*>) => any,
}
): RenderResult {}Deeply render given React element and returns helpers to query the output.
import { render } from 'react-native-testing-library';
const { getByTestId, getByName /*...*/ } = render(<Component />);Returns a RenderResult object with following properties:
A method returning a ReactTestInstance with matching testID prop. Throws when no matches.
Note: most methods like this one return a ReactTestInstance with following properties that you may be interested in:
type ReactTestInstance = {
type: string | Function,
props: { [propName: string]: any },
parent: null | ReactTestInstance,
children: Array<ReactTestInstance | string>,
};A method returning a ReactTestInstance with matching name – may be a string or React Element. Throws when no matches.
A method returning an array of ReactTestInstances with matching name – may be a string or React Element.
A method returning a ReactTestInstance with matching text – may be a string or regular expression. Throws when no matches.
A method returning an array of ReactTestInstances with matching text – may be a string or regular expression.
A method returning a ReactTestInstance with matching props object. Throws when no matches.
A method returning an array of ReactTestInstances with matching props object.
Re-render the in-memory tree with a new root element. This simulates a React update at the root. If the new element has the same type and key as the previous element, the tree will be updated; otherwise, it will re-mount a new tree.
Unmount the in-memory tree, triggering the appropriate lifecycle events
When using React context providers, like Redux Provider, you'll likely want to wrap rendered component with them. In such cases it's convenient to create your custom render method. Follow this great guide on how to set this up.
Get the rendered component JSON representation, e.g. for snapshot testing.
Shallowly render given React component. Since it doesn't return helpers to query the output, it's mostly advised to used for snapshot testing (short snapshots are best for code reviewers).
import { shallow } from 'react-native-testing-library';
test('Component has a structure', () => {
const { output } = shallow(<Component />);
expect(output).toMatchSnapshot();
});Invokes named event handler on the element or parent element in the tree.
import { View } from 'react-native';
import { render, fireEvent } from 'react-native-testing-library';
import { MyComponent } from './MyComponent';
const onEventMock = jest.fn();
const { getByTestId } = render(
<MyComponent testID="custom" onMyCustomEvent={onEventMock} />
);
fireEvent(getByTestId('custom'), 'myCustomEvent');Invokes press event handler on the element or parent element in the tree.
import { View, Text, TouchableOpacity } from 'react-native';
import { render, fireEvent } from 'react-native-testing-library';
const onPressMock = jest.fn();
const { getByTestId } = render(
<View>
<TouchableOpacity onPress={onPressMock} testID="button">
<Text>Press me</Text>
</TouchableOpacity>
</View>
);
fireEvent.press(getByTestId('button'));Invokes changeText event handler on the element or parent element in the tree.
import { View, TextInput } from 'react-native';
import { render, fireEvent } from 'react-native-testing-library';
const onChangeTextMock = jest.fn();
const CHANGE_TEXT = 'content';
const { getByTestId } = render(
<View>
<TextInput testID="text-input" onChangeText={onChangeTextMock} />
</View>
);
fireEvent.changeText(getByTestId('text-input'), CHANGE_TEXT);Invokes scroll event handler on the element or parent element in the tree.
import { ScrollView, TextInput } from 'react-native';
import { render, fireEvent } from 'react-native-testing-library';
const onScrollMock = jest.fn();
const eventData = {
nativeEvent: {
contentOffset: {
y: 200,
},
},
};
const { getByTestId } = render(
<ScrollView testID="scroll-view" onScroll={onScrollMock}>
<Text>XD</Text>
</ScrollView>
);
fireEvent.scroll(getByTestId('scroll-view'), eventData);Defined as:
function waitForExpect<T: *>(
expectation: () => T,
timeout: number = 4500,
interval: number = 50
): Promise<T> {}Wait for non-deterministic periods of time until your element appears or times out. waitForExpect periodically calls expectation every interval milliseconds to determine whether the element appeared or not.
import { render, waitForElement } from 'react-testing-library';
test('waiting for an Banana to be ready', async () => {
const { getByText } = render(<Banana />);
await waitForElement(() => getByText('Banana ready'));
});If you're using Jest's Timer Mocks, remember not to use async/await syntax as it will stall your tests.
Log prettified shallowly rendered component or test instance (just like snapshot) to stdout.
import { debug } from 'react-native-testing-library';
debug(<Component />);
debug.shallow(<Component />); // an alias for `debug`logs:
<TouchableOpacity
activeOpacity={0.2}
onPress={[Function bound fn]}
>
<TextComponent
text="Press me"
/>
</TouchableOpacity>There's also debug.deep that renders deeply to stdout.
import { debug } from 'react-native-testing-library';
debug.deep(<Component />);
debug.deep(toJSON(), 'actually debug JSON too'); // useful when Component state changeslogs:
<View
accessible={true}
isTVSelectable={true}
onResponderGrant={[Function bound touchableHandleResponderGrant]}
// ... more props
style={
Object {
\\"opacity\\": 1,
}
}
>
<Text>
Press me
</Text>
</View>Optionally you can provide a string message as a second argument to debug, which will be displayed right after the component.
Wait for microtasks queue to flush. Useful if you want to wait for some promises with async/await.
import { flushMicrotasksQueue, render } from 'react-native-testing-library';
test('fetch data', async () => {
const { getByText } = render(<FetchData />);
getByText('fetch');
await flushMicrotasksQueue();
expect(getByText('fetch').props.title).toBe('loaded');
});Each of the get APIs listed in the render section above have a complimentary query API. The get APIs will throw errors if a proper node cannot be found. This is normally the desired effect. However, if you want to make an assertion that an element is not present in the hierarchy, then you can use the query API instead:
import { render } from 'react-native-testing-library';
const { queryByText } = render(<Form />);
const submitButton = queryByText('submit');
expect(submitButton).toBeNull(); // it doesn't existEach of the query APIs have a corresponding queryAll version that always returns an Array of matching nodes. getAll is the same but throws when the array has a length of 0.
import { render } from 'react-native-testing-library';
const { queryAllByText } = render(<Forms />);
const submitButtons = queryAllByText('submit');
expect(submitButtons).toHaveLength(3); // expect 3 elements