Refactor Firebase Admin Stubbing

[samtstern]

Description

Fixes issue #1454

This investigation took me very deep and along the way I also:

• Added some standardization for how we resolve developer node modules and made sure we log them.
• Simplified some of our logging code.

Scenarios Tested

Using these functions to test:

const functions = require("firebase-functions");
const admin = require('firebase-admin');

const app = admin.initializeApp();

exports.writeThroughAdmin = functions.https.onRequest(async (req, res) => {
    const firestore = admin.firestore();
    const ref = firestore.doc("info/test");
    await ref.set({ hello: (new Date().toISOString()) });
    ref.get().then((snap) => {
        res.json({ data: snap.data() });
    });
});

exports.writeThroughApp = functions.https.onRequest(async (req, res) => {
    const firestore = app.firestore();
    const ref = firestore.doc("info/test");
    await ref.set({ hello: (new Date().toISOString()) });
    ref.get().then((snap) => {
        res.json({ data: snap.data() });
    });
});

exports.firestoreReaction = functions.firestore.document("info/test").onWrite(async (change, ctx) => {
    console.log('~~~~~~~~~~ FIRESTORE WRITE ~~~~~~~~~~');
    return true;
});

I also added a unit test that verifies the same behavior.

Sample Commands

N/A

[coveralls]

Coverage increased (+0.1%) to 61.884% when pulling 6bf6372 on ss-fix-1454 into c871443 on master.

[yuchenshi]

To be honest, I still cannot get my head around the three layers of stubbing involved in this PR (JS proxy, Node.js require cache, fake creds) and I'm not familiar with the code base. But I'm sure it will be fine somehow.

WANT_LGTM=abeisgoat

[samtstern]

@yuchenshi thanks for taking a look. I agree with waiting for @abeisgoat

Waiting on @abeisgoat to take a final pass.

[abeisgoat]

Looks pretty good as long as there aren't any logic changes in the big function