Testing a fetch.catch in custom hook

Question

I've got this custom hook:

import React from 'react';
import { useMessageError } from 'components/Message/UseMessage';

export interface Country {
  code: string;
  name: string;
}

export default function useCountry(): Array<Country> {
  const [countries, setCountries] = React.useState<Country[]>([]);
  const { showErrorMessage } = useMessageError();

  React.useEffect(() => {
    fetch('/api/countries', {
      method: 'GET',
    })
      .then(data => data.json())
      .then(function(data) {
        // ..
      })
      .catch(() => showErrorMessage());
  }, []);

  return countries;
}

I want to test catching an error if there will be invalid response. With that, error message should appear thanks to showErrorMessage(). And I've got this test:

const showErrorMessage = jest.fn();

jest.mock('components/Message/UseMessage', () => ({
  useMessageError: () => ({
    showErrorMessage: showErrorMessage,
  }),
}));

import useCountry from 'components/Country/useCountry';
import { renderHook } from '@testing-library/react-hooks';
import { enableFetchMocks } from 'jest-fetch-mock';
enableFetchMocks();

describe('The useCountry hook', () => {
  it('should show error message', async () => {
    jest.spyOn(global, 'fetch').mockImplementation(() =>
      Promise.resolve({
        json: () => Promise.reject(),
      } as Response),
    );

    const { result, waitForNextUpdate } = renderHook(() => useCountry());
    await waitForNextUpdate();

    expect(fetch).toHaveBeenCalled();
    expect(showErrorMessage).toHaveBeenCalled();
    expect(result.current).toEqual([]);
  });
});

But with that, I'm getting an error:

Timeout - Async callback was not invoked within the 5000ms timeout specified by jest.setTimeout.Timeout - Async callback was not invoked within the 5000ms timeout specified by jest.setTimeout.Error

What I'm doing wrong in here? I assume it is somehow related with await waitForNextUpdate();, but I really don't know for sure and how to manage with it.

Answer 1

waitForNextUpdate() waits for next update but your hook does not trigger it since it only calls showErrorMessage(). Take a look at this sandbox

As a straightforward solution something that triggers an update can be added:

  React.useEffect(() => {
    fetch('/api/countries', {
      method: 'GET',
    })
      .then(data => data.json())
      .then(function(data) {
        // ..
      })
      .catch(() => { 
        showErrorMessage();
        // trigger update in any suitable way, for example:
        setCountries([]); 
      });
  }, []);

But it may be better to refactor it in some way. For example, you could use a separate hook and state for errors:

export default function useCountry(): Array<Country> {
  const [countries, setCountries] = React.useState<Country[]>([]);
  const [error, setError] = React.useState(null);
  const { showErrorMessage } = useMessageError();

  React.useEffect(() => {
    fetch('/api/countries', {
      method: 'GET',
    })
      .then(data => data.json())
      .then(function(data) {
        // ..
      })
      .catch(() => setError(true));
  }, []);
  
  React.useEffect(() => {
    if (error) {
      showErrorMessage()
    }
  }, [error]);

  return countries;
}