I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

Why do you need a create in tests while there are no create in actual Transaction?

set will take care of creating the doc if it does not exist.

Are we talking about different Transaction?:

export class Transaction {
   ...
   /**
     * Create the document referred to by the provided `DocumentReference`.
     * The operation will fail the transaction if a document exists at the
     * specified location.
     *
     * @param documentRef A reference to the document to be create.
     * @param data The object data to serialize as the document.
     * @return This `Transaction` instance. Used for chaining method calls.
     */
    create<T>(documentRef: DocumentReference<T>, data: T): Transaction;
}

Transaction.create is used by production code, so when it's running under firestore emulator with @firestore/testing used - I'd expect that all create/set/update/delete would work.

Yes, we are talking about different transactions.

The Transaction you paste is from the Node SDK. It's a server SDK. What @firebase/testing creates for you is a client side JS Firestore. They are different.

I see you were no happy with my reply earlier, I apologize for not explaining this with deserved details.

It's unfortunate in this context that @firebase/testing is actually returning an instance of the web SDK, not the server-side Node.js SDK. #2112 catalogues all the differences between them.

In some sense this is a duplicate of #1324. Rules testing is an interesting new motivating use case for this though so we'll bump our internal priority on this in the backlog. PRs welcome in the meantime :-).

This is b/129358230 internally.

@wu-hui, got it. Thank you.

Honestly speaking it's not that obvious where @firebase/testing is belong (client/server side). I've found it on https://firebase.google.com/docs/rules/unit-tests#firestore, and first assumptions is that it's "good start for unit tests" (on the backend).

But there're a bunch of issues when @firebase/testing is used this way (there is another one: firebase/firebase-tools#1971).

Only some issue on the github hinted me that firebase emulator does work well with firebase-admin (so no need in @firebase/testing) when FIRESTORE_EMULATOR_HOST is set.