Cannot add a promise implementation on jest mock function outside test block

Question

const mockedLogin = jest.fn(() => Promise.resolve()); //does not work if implementation is done here: "cannot read then of undefined"

jest.mock("../../hooks/useAuth", () => {
  return () => ({
    login: mockedLogin,
  });
});

test("submitting the form calls onSubmit with username and password", async () => {
  mockedLogin.mockImplementation(() => Promise.resolve()); //works fine here
  render(<Login />);
  const username = "name";
  const password = "i need no password";

  await userEvent.type(screen.getByLabelText(/username/i), username);
  await userEvent.type(screen.getByLabelText(/password/i), password);
  await userEvent.click(screen.getByRole("button", { name: /submit/i }));

  expect(mockedLogin).toHaveBeenCalledWith({
    username,
    password,
  });
  expect(mockedLogin).toHaveBeenCalledTimes(1);
});

I am trying to mock login function returned by a custom hook. The login function returns a promise. If I use mockImplementation inside the test block it works fine but if I use it outside of the test block mockedLogin returns undefined.

Answer 1

Have you tried:

const mockedLogin = jest.fn().mockResolvedValue();