callstack__react-native-testing-library/website/docs/API.md

id, title

id	title
api	API

This page gathers public API of React Native Testing Library along with usage examples.

render

• Example code

Defined as:

function render(
  component: React.Element<any>,
  options?: {
    /* A React Component that renders `component` as children */
    wrapper?: React.ComponentType<any>,
    /* You won't often use this, but it's helpful when testing refs */
    createNodeMock: (element: React.Element<any>) => any,
  }
): RenderResult {}

Deeply renders given React element and returns helpers to query the output components structure.

import { render } from '@testing-library/react-native';
import { QuestionsBoard } from '../QuestionsBoard';

test('should verify two questions', () => {
  const { queryAllByA11yRole } = render(<QuestionsBoard {...props} />);
  const allQuestions = queryAllByA11yRole('header');

  expect(allQuestions).toHaveLength(2);
});

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.

The render method returns a RenderResult object that has a few properties:

...queries

The most important feature of render is providing a set of helpful queries that allow you to find certain elements in the view hierarchy.

See Queries for a complete list.

Example

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

const { getByText, queryByA11yStates } = render(<Component />);

update

Also available under rerender alias

update(element: React.Element<any>): void
rerender(element: React.Element<any>): void

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. This is useful when testing for componentDidUpdate behavior, by passing updated props to the component.

Example code

unmount

unmount(): void

Unmount the in-memory tree, triggering the appropriate lifecycle events.

:::note Usually you should not need to call unmount as it is done automatically if your test runner supports afterEach hook (like Jest, mocha, Jasmine). :::

debug

debug(message?: string): void

Pretty prints deeply rendered component passed to render with optional message on top.

const { debug } = render(<Component />);

debug('optional message');

logs optional message and colored JSX:

optional message

<View
  onPress={[Function bound fn]}
>
  <Text>Press me</Text>
</View>

debug.shallow

Pretty prints shallowly rendered component passed to render with optional message on top.

toJSON

toJSON(): ReactTestRendererJSON | null

Get the rendered component JSON representation, e.g. for snapshot testing.

cleanup

const cleanup: () => void;

Unmounts React trees that were mounted with render.

:::info Please note that this is done automatically if the testing framework you're using supports the afterEach global (like mocha, Jest, and Jasmine). If not, you will need to do manual cleanups after each test. :::

For example, if you're using the jest testing framework, then you would need to use the afterEach hook like so:

import { cleanup, render } from '@testing-library/react-native/pure';
import { View } from 'react-native';

afterEach(cleanup);

it('renders a view', () => {
  render(<View />);
  // ...
});

The afterEach(cleanup) call also works in describe blocks:

describe('when logged in', () => {
  afterEach(cleanup);

  it('renders the user', () => {
    render(<SiteHeader />);
    // ...
  });
});

Failing to call cleanup when you've called render could result in a memory leak and tests which are not "idempotent" (which can lead to difficult to debug errors in your tests).

The alternative to cleanup is balancing every render with an unmount method call.

fireEvent

fireEvent(element: ReactTestInstance, eventName: string, ...data: Array<any>): void

Fires native-like event with data.

Invokes a given event handler (whether native or custom) on the element, bubbling to the root of the rendered tree.

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

test('fire changeText event', () => {
  const onEventMock = jest.fn();
  const { getByPlaceholderText } = render(
    // MyComponent renders TextInput which has a placeholder 'Enter details'
    // and with `onChangeText` bound to handleChangeText
    <MyComponent handleChangeText={onEventMock} />
  );

  fireEvent(getByPlaceholderText('change'), 'onChangeText', 'ab');
  expect(onEventMock).toHaveBeenCalledWith('ab');
});

:::note Please note that from version 7.0 fireEvent performs checks that should prevent events firing on disabled elements. :::

An example using fireEvent with native events that aren't already aliased by the fireEvent api.

import { TextInput, View } from 'react-native';
import { fireEvent, render } from '@testing-library/react-native';

const onBlurMock = jest.fn();

const { getByPlaceholderText } = render(
  <View>
    <TextInput placeholder="my placeholder" onBlur={onBlurMock} />
  </View>
);

// you can omit the `on` prefix
fireEvent(getByPlaceholderText('my placeholder'), 'blur');

fireEvent[eventName]

fireEvent[eventName](element: ReactTestInstance, ...data: Array<any>): void

Convenience methods for common events like: press, changeText, scroll.

fireEvent.press: (element: ReactTestInstance) => void

Invokes press event handler on the element or parent element in the tree.

import { View, Text, TouchableOpacity } from 'react-native';
import { render, fireEvent } from '@testing-library/react-native';

const onPressMock = jest.fn();

const { getByText } = render(
  <View>
    <TouchableOpacity onPress={onPressMock}>
      <Text>Press me</Text>
    </TouchableOpacity>
  </View>
);

fireEvent.press(getByText('Press me'));
expect(onPressMock).toHaveBeenCalled();

fireEvent.changeText: (element: ReactTestInstance, ...data: Array<any>) => void

Invokes changeText event handler on the element or parent element in the tree.

import { View, TextInput } from 'react-native';
import { render, fireEvent } from '@testing-library/react-native';

const onChangeTextMock = jest.fn();
const CHANGE_TEXT = 'content';

const { getByPlaceholderText } = render(
  <View>
    <TextInput placeholder="Enter data" onChangeText={onChangeTextMock} />
  </View>
);

fireEvent.changeText(getByPlaceholderText('Enter data'), CHANGE_TEXT);

fireEvent.scroll: (element: ReactTestInstance, ...data: Array<any>) => void

Invokes scroll event handler on the element or parent element in the tree.

On a ScrollView

import { ScrollView, Text } from 'react-native';
import { render, fireEvent } from '@testing-library/react-native';

const onScrollMock = jest.fn();
const eventData = {
  nativeEvent: {
    contentOffset: {
      y: 200,
    },
  },
};

const { getByText } = render(
  <ScrollView onScroll={onScrollMock}>
    <Text>XD</Text>
  </ScrollView>
);

fireEvent.scroll(getByText('scroll-view'), eventData);

On a FlatList

import { FlatList, View } from 'react-native';
import { render, fireEvent } from '@testing-library/react-native';

const onEndReached = jest.fn();
const { getByTestId } = render(
  <FlatList
    data={Array.from({ length: 10 }, (_, key) => ({ key: `${key}` }))}
    renderItem={() => <View style={{ height: 500, width: 100 }} />}
    onEndReached={onEndReached}
    onEndReachedThreshold={0.2}
    testID="flat-list"
  />
);
const eventData = {
  nativeEvent: {
    contentOffset: {
      y: 500,
    },
    contentSize: {
      // Dimensions of the scrollable content
      height: 500,
      width: 100,
    },
    layoutMeasurement: {
      // Dimensions of the device
      height: 100,
      width: 100,
    },
  },
};

fireEvent.scroll(getByTestId('flat-list'), eventData);
expect(onEndReached).toHaveBeenCalled();

waitFor

• Example code

Defined as:

function waitFor<T>(
  expectation: () => T,
  { timeout: number = 4500, interval: number = 50 }
): Promise<T> {}

Waits for non-deterministic periods of time until your element appears or times out. waitFor periodically calls expectation every interval milliseconds to determine whether the element appeared or not.

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

test('waiting for an Banana to be ready', async () => {
  const { getByText } = render(<Banana />);

  await waitFor(() => getByText('Banana ready'));
});

:::info In order to properly use waitFor you need at least React >=16.9.0 (featuring async act) or React Native >=0.60 (which comes with React >=16.9.0). :::

If you're using Jest's Timer Mocks, remember not to await the return of waitFor as it will stall your tests.

waitForElementToBeRemoved

• Example code

Defined as:

function waitForElementToBeRemoved<T>(
  expectation: () => T,
  { timeout: number = 4500, interval: number = 50 }
): Promise<T> {}

Waits for non-deterministic periods of time until queried element is removed or times out. waitForElementToBeRemoved periodically calls expectation every interval milliseconds to determine whether the element has been removed or not.

import {
  render,
  waitForElementToBeRemoved,
} from '@testing-library/react-native';

test('waiting for an Banana to be removed', async () => {
  const { getByText } = render(<Banana />);

  await waitForElementToBeRemoved(() => getByText('Banana ready'));
});

This method expects that the element is initally present in the render tree and then is removed from it. If the element is not present when you call this method it throws an error.

You can use any of getBy, getAllBy, queryBy and queryAllBy queries for expectation parameter.

:::info In order to properly use waitForElementToBeRemoved you need at least React >=16.9.0 (featuring async act) or React Native >=0.60 (which comes with React >=16.9.0). :::

If you're using Jest's Timer Mocks, remember not to use async/await syntax as it will stall your tests.

within, getQueriesForElement

• Example code

Defined as:

function within(instance: ReactTestInstance): Queries
function getQueriesForElement(instance: ReactTestInstance): Queries

within (also available as getQueriesForElement alias) performs queries scoped to given element.

:::note Please note that additional render specific operations like update, unmount, debug, toJSON are not included. :::

const detailsScreen = within(getByA11yHint('Details Screen'));
expect(detailsScreen.getByText('Some Text')).toBeTruthy();
expect(detailsScreen.getByDisplayValue('Some Value')).toBeTruthy();
expect(detailsScreen.queryByA11yLabel('Some Label')).toBeTruthy();
await expect(detailsScreen.findByA11yHint('Some Label')).resolves.toBeTruthy();

Use cases for scoped queries include:

• queries scoped to a single item inside a FlatList containing many items
• queries scoped to a single screen in tests involving screen transitions (e.g. with react-navigation)

query APIs

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 '@testing-library/react-native';

const { queryByText } = render(<Form />);
const submitButton = queryByText('submit');
expect(submitButton).toBeNull(); // it doesn't exist

queryAll APIs

Each 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 '@testing-library/react-native';

const { queryAllByText } = render(<Forms />);
const submitButtons = queryAllByText('submit');
expect(submitButtons).toHaveLength(3); // expect 3 elements

act

Useful function to help testing components that use hooks API. By default any render, update, fireEvent, and waitFor calls are wrapped by this function, so there is no need to wrap it manually. This method is re-exported from react-test-renderer.