Mock firebase for API route authentication

[tettoffensive]

I have an API route that I want to test /pages/api/login.ts:

import firebase from 'firebase/app';
import 'firebase/auth';
import withSession from '~/lib/withSession';
import initFirebase from '~/lib/initFirebase';
import { AuthStatus } from '~/lib/useUser';

const actionCodeSettings = {
  url: `${process.env.baseUrl}/validate`,
  // This must be true.
  handleCodeInApp: true,
};

export default withSession(async (req, res) => {
  const { email } = await req.body;

  initFirebase();

  try {
    await firebase.auth().sendSignInLinkToEmail(email, actionCodeSettings);
    const user = {
      authStatus: AuthStatus.Pending,
      email,
    };
    req.session.set('user', user);
    await req.session.save();
    res.json(user);
  } catch (error) {
    res.status(500).json(error);
  }
});

I am trying to test it with the following, however, I would like to mock firebase so that I can get expectations such as "sends email sign in link" to pass.

import http from 'http';
import listen from 'test-listen';
import { apiResolver } from 'next/dist/next-server/server/api-utils';
import fetch from 'isomorphic-unfetch';
import { AuthStatus } from '../../../lib/useUser';

import * as handler from '../login';

describe('/api/login handler', () => {
  let server;
  let url;

  beforeAll(async (done) => {
    server = http.createServer((req, res) => apiResolver(req, res, undefined, handler, undefined));
    url = await listen(server);
    done();
  });

  afterAll((done) => {
    server.close(done);
  });
  it('should return 500 if required email is missing', async () => {
    const response = await fetch(url);
    expect(response.status).toBe(500);
  });

  it('sends email sign in link', async () => {
    const inputs = { email: '[email protected]' };
    const response = await fetch(url, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ ...inputs }),
    });
    const jsonResult = await response.json();

    expect(response.status).toBe(500);
    expect(jsonResult).toMatchObject({
      authStatus: AuthStatus.Pending,
      email: inputs.email,
    });
  });
});

I've tried creating a __mocks__/firebase/auth.js file. But according to jest docs:

Note: In order to mock properly, Jest needs jest.mock('moduleName') to be in the same scope as the require/import statement.

But my firebase import statements are in my API route code, not in my test file.

Any suggestions as to how to get this working? I'm open to suggestions if this is not a good way to test API routes.