Testing custom hook - not wrapped in act warning - testing

Question

I' trying to test a custom hook but I receive this warning message
console.error node_modules/#testing-library/react-hooks/lib/core/console.js:19
Warning: An update to TestComponent inside a test was not wrapped in act(...).
When testing, code that causes React state updates should be wrapped into act(...):
act(() => {
/* fire events that update state */
});
/* assert on the output */
This ensures that you're testing the behavior the user would see in the browser.
This is my custom hook
import { useState, useEffect } from 'react'
import io from 'socket.io-client'
import config from './../../../../config'
const useNotificationsSocket = (user) => {
const [socket, setSocket] = useState(null)
const [numUnreadMessages, setNumUnreadMessages] = useState(0)
const configureSocket = socket => {
socket.on('connect', () => {
const data = {
user: user,
}
socket.emit('user joined', data)
})
socket && socket.on('messages updated', (data) => {
//console.log(data)
setNumUnreadMessages(data.numUnreadMessages)
})
}
useEffect(() => {
const fetchSocket = async () => {
const s = await io(config.nSocket.url, {transports: ['websocket']})
configureSocket(s)
setSocket(s)
}
// Check that user is not an empty object as this causes a crash.
user && user.Id && fetchSocket()
}, [user])
return [socket, numUnreadMessages]
}
export { useNotificationsSocket }
and this is the test
import { renderHook, act } from '#testing-library/react-hooks'
import { useNotificationsSocket } from './../hooks/useNotificationsSocket'
jest.mock('socket.io-client')
describe('useNotificationsSocket', () => {
it('returns a socket and numUnreadMessages', async () => {
const user = { Id: '1' }
const { result } = renderHook(() => useNotificationsSocket(user))
expect(result).not.toBeNull()
})
})
I've tried importing act and wrapping the code in a call to act but however I try to wrap the code I still get a warning and can't figure out how I should use act in this case.

Answer 1

Your hook is asynchronous, so you need to await its response:
describe('useNotificationsSocket', () => {
it('returns a socket and numUnreadMessages', async () => {
const user = { Id: '1' }
const { result } = renderHook(() => useNotificationsSocket(user))
await waitFor(() => expect(result).not.toBeNull())
})
})
Additionally, if you define multiple tests, you may encounter your original error if you fail to unmount the hook. At least this appears to be the behaviour in #testing-library/react v13.3.0. You can solve this by unmounting the hook when your test completes:
describe('useNotificationsSocket', () => {
it('returns a socket and numUnreadMessages', async () => {
const user = { Id: '1' }
const { result, unmount } = renderHook(() => useNotificationsSocket(user))
await waitFor(() => expect(result).not.toBeNull())
unmount()
})
})