How to unit test a function that depends on Firebase reference?

Question

I want to unit test a function in my application that calls and updates a Firebase reference. The problem I am facing is that when I try to run the test and import the file that contains the function, I get the following error SyntaxError: Unexpected token u in JSON at position 0 which points to the line in my function file that imports my reference to Firebase.

I am using Webpack and Babel on this project, so I tried setting a resolve.alias in the webpack.config file which worked when the application was running, but did not work when I ran npm test . At this point I'm at a loss as to how I can mock out the Firebase reference so I can test the other functions of the function. Here's some sample code:

constants/index.js

import firebase from 'firebase';
const firebaseConfig = JSON.parse(unescape(`${config.FIREBASE_CONFIG}`));

const mainApp = firebase.initializeApp(firebaseConfig);

export const ref = mainApp.database().ref();

actions/settings.js

import * as actions from './';
import { ref } from '../constants';

export const updateSetting = (e, value) =>
  (dispatch) => {
     ref.child('setting')
      .set(value)
      .then(() => {
        dispatch(actions.confirmFBSave());
      })
      .catch((err) => {
        dispatch(actions.failFBSave({ text: err.code }));
      });
  };

Answer 1

What testing framework are you using Qunit, jasmine, mocha? With AngularFire and Angular it is much easier because you can pass a mock class in at DI, but I have also tested non angular js for server side. Then I used Sinon to get mock initializeApp and return a Mock firebase app.

You could also try https://github.com/thlorenz/proxyquire I didn't need to go that far, but I have seen it suggested. That way you are essentially intercepting the import and swap it out for something you can test with.