Adjust test util withTestDoc() to accept initial data

[rsgowman]

Similar to withTestCollection.

[mikelehen]

So TypeScript actually supports a mechanism for method overloads. It's a bit wacky (you basically list out all the overload signatures and then implement a function whose signature is a superset of all the overloads and then dynamically handle the various possible calls at runtime).

So that would look something like:

export type WithTestDocCallback = (doc: firestore.DocumentReference) => Promise<void>;
export function withTestDoc(
  persistence: boolean,
  fn: WithTestDocCallback
);
export function withTestDoc(
  persistence: boolean,
  initialData: firestore.DocumentData,
  fn: WithTestDocCallback
);
export function withTestDoc(
  persistence: boolean,
  initialDataOrFn: firestore.DocumentData | WithTestDocCallback,
  fn?: WithTestDocCallback
): Promise<void> {
  let initialData = null;
  if (fn) {
    initialData = initialDataOrFn;
  } else {
    fn = initialDataOrFn as WithTestDocCallback;
  }
  return withTestDb(persistence, db => {
    const docRef: firestore.DocumentReference = db
      .collection('test-collection')
      .doc();
    if (initialData) {
      return docRef.set(initialData).then(() => fn(docRef));
    } else {
      return fn(docRef);
    }
  });
}

And then all the places you're passing null can go back to how they were before.

Sorry, this is what I had in my mind when I asked you to do the TODO and would have been a much easier migration. Though I like that you've gone ahead and cleaned up a bunch of tests to leverage initialData. That's a nice improvement. Thanks!

[rsgowman]

Ah, I see. Done.

It's just as well I initially did it this way though. Otherwise, I would've been tempted to not do the cleanups. :)

[schmidt-sebastian]

Rich, when you change this to Master you will also notice that this now conflicts considerably with the changes that I merged in #667

I would suggest that you pick your changes over mine and fix the remaining lint errors manually.

[mikelehen]

LGTM

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