react-testing-library/src/__tests__/end-to-end.js

import * as React from 'react'
import {render, waitForElementToBeRemoved, screen, waitFor} from '../'

describe.each([
  ['real timers', () => jest.useRealTimers()],
  ['fake legacy timers', () => jest.useFakeTimers('legacy')],
  ['fake modern timers', () => jest.useFakeTimers('modern')],
])(
  'it waits for the data to be loaded in a macrotask using %s',
  (label, useTimers) => {
    beforeEach(() => {
      useTimers()
    })

    afterEach(() => {
      jest.useRealTimers()
    })

    const fetchAMessageInAMacrotask = () =>
      new Promise(resolve => {
        // we are using random timeout here to simulate a real-time example
        // of an async operation calling a callback at a non-deterministic time
        const randomTimeout = Math.floor(Math.random() * 100)
        setTimeout(() => {
          resolve({returnedMessage: 'Hello World'})
        }, randomTimeout)
      })

    function ComponentWithMacrotaskLoader() {
      const [state, setState] = React.useState({data: undefined, loading: true})
      React.useEffect(() => {
        let cancelled = false
        fetchAMessageInAMacrotask().then(data => {
          if (!cancelled) {
            setState({data, loading: false})
          }
        })

        return () => {
          cancelled = true
        }
      }, [])

      if (state.loading) {
        return <div>Loading...</div>
      }

      return (
        <div data-testid="message">
          Loaded this message: {state.data.returnedMessage}!
        </div>
      )
    }

    test('waitForElementToBeRemoved', async () => {
      render(<ComponentWithMacrotaskLoader />)
      const loading = () => screen.getByText('Loading...')
      await waitForElementToBeRemoved(loading)
      expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
    })

    test('waitFor', async () => {
      render(<ComponentWithMacrotaskLoader />)
      await waitFor(() => screen.getByText(/Loading../))
      await waitFor(() => screen.getByText(/Loaded this message:/))
      expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
    })

    test('findBy', async () => {
      render(<ComponentWithMacrotaskLoader />)
      await expect(screen.findByTestId('message')).resolves.toHaveTextContent(
        /Hello World/,
      )
    })
  },
)

describe.each([
  ['real timers', () => jest.useRealTimers()],
  ['fake legacy timers', () => jest.useFakeTimers('legacy')],
  ['fake modern timers', () => jest.useFakeTimers('modern')],
])(
  'it waits for the data to be loaded in many microtask using %s',
  (label, useTimers) => {
    beforeEach(() => {
      useTimers()
    })

    afterEach(() => {
      jest.useRealTimers()
    })

    const fetchAMessageInAMicrotask = () =>
      Promise.resolve({
        status: 200,
        json: () => Promise.resolve({title: 'Hello World'}),
      })

    function ComponentWithMicrotaskLoader() {
      const [fetchState, setFetchState] = React.useState({fetching: true})

      React.useEffect(() => {
        if (fetchState.fetching) {
          fetchAMessageInAMicrotask().then(res => {
            return (
              res
                .json()
                // By spec, the runtime can only yield back to the event loop once
                // the microtask queue is empty.
                // So we ensure that we actually wait for that as well before yielding back from `waitFor`.
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => data)
                .then(data => {
                  setFetchState({todo: data.title, fetching: false})
                })
            )
          })
        }
      }, [fetchState])

      if (fetchState.fetching) {
        return <p>Loading..</p>
      }

      return (
        <div data-testid="message">Loaded this message: {fetchState.todo}</div>
      )
    }

    test('waitForElementToBeRemoved', async () => {
      render(<ComponentWithMicrotaskLoader />)
      const loading = () => screen.getByText('Loading..')
      await waitForElementToBeRemoved(loading)
      expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
    })

    test('waitFor', async () => {
      render(<ComponentWithMicrotaskLoader />)
      await waitFor(() => {
        screen.getByText('Loading..')
      })
      await waitFor(() => {
        screen.getByText(/Loaded this message:/)
      })
      expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
    })

    test('findBy', async () => {
      render(<ComponentWithMicrotaskLoader />)
      await expect(screen.findByTestId('message')).resolves.toHaveTextContent(
        /Hello World/,
      )
    })
  },
)

describe.each([
  ['real timers', () => jest.useRealTimers()],
  ['fake legacy timers', () => jest.useFakeTimers('legacy')],
  ['fake modern timers', () => jest.useFakeTimers('modern')],
])(
  'it waits for the data to be loaded in a microtask using %s',
  (label, useTimers) => {
    beforeEach(() => {
      useTimers()
    })

    afterEach(() => {
      jest.useRealTimers()
    })

    const fetchAMessageInAMicrotask = () =>
      Promise.resolve({
        status: 200,
        json: () => Promise.resolve({title: 'Hello World'}),
      })

    function ComponentWithMicrotaskLoader() {
      const [fetchState, setFetchState] = React.useState({fetching: true})

      React.useEffect(() => {
        if (fetchState.fetching) {
          fetchAMessageInAMicrotask().then(res => {
            return res.json().then(data => {
              setFetchState({todo: data.title, fetching: false})
            })
          })
        }
      }, [fetchState])

      if (fetchState.fetching) {
        return <p>Loading..</p>
      }

      return (
        <div data-testid="message">Loaded this message: {fetchState.todo}</div>
      )
    }

    test('waitForElementToBeRemoved', async () => {
      render(<ComponentWithMicrotaskLoader />)
      const loading = () => screen.getByText('Loading..')
      await waitForElementToBeRemoved(loading)
      expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
    })

    test('waitFor', async () => {
      render(<ComponentWithMicrotaskLoader />)
      await waitFor(() => {
        screen.getByText('Loading..')
      })
      await waitFor(() => {
        screen.getByText(/Loaded this message:/)
      })
      expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
    })

    test('findBy', async () => {
      render(<ComponentWithMicrotaskLoader />)
      await expect(screen.findByTestId('message')).resolves.toHaveTextContent(
        /Hello World/,
      )
    })
  },
)