hook.ts
function useFileRetrieval() {
  const [retrieving, setIsRetrieving] = useState(false);
  const [success, setSuccessMessage] = useState<string | null>(null);
  const setError = useSetRecoilState(errorState);
  const authenticationToken = useContext(AuthContext);

  async function retrieveFile(fileLink: string) {
    const fileLinkIncludesHttp = fileLink.toLocaleLowerCase().includes('http');
    const fileLinkIncludesBlob = fileLink.toLocaleLowerCase().includes('blob://');

    if (fileLinkIncludesHttp) {
      window.open(fileLink, '_blank', 'noreferrer');
      return;
    }

    if (fileLinkIncludesBlob) {
      // do nothing as link isn't a web address, and also doesn't contain custom blob string
      return;
    }

    const [index, filename] = fileLink.split('/');

    setIsRetrieving(true);
    try {
      await getFile(index, filename, authenticationToken, setError);
      setError(null);
      setSuccessMessage('File retrieved successfully.');
    } catch (error) {
      setError('Error retrieving file.');
      setSuccessMessage(null);
    } finally {
      setIsRetrieving(false);
    }
  }

  return {
    retrieveFile,
    retrieving,
    success,
  };
}

hook.test.ts
it('should set retrieving to true while retrieving the file and to false after', async () => {
    const { result } = renderHook(() => useFileRetrieval(), { wrapper: Wrapper });
    const { retrieveFile, retrieving } = result.current;

    getFileMock.mockReturnValue(
      new Promise<void>(resolve => {
        setTimeout(() => {
          expect(retrieving).toBe(true);
          resolve();
        }, 100);
      }),
    );

    await act(async () => {
      await retrieveFile('index/fileName');
    });

    expect(retrieving).toBe(false);
  });