Make it easier to reliably test data observers

In my experience, testing data observers is somewhat brittle. Even with explicit transactions I sometimes get "delayed" notifications that have been triggered by the previous operation.

Let's take this test (ObjectBox 2.2.0 + RxJava 2):

boxStore.runInTx {
    boxStore.boxFor(SomeEntity::class.java).put(SomeEntity())
}

val testObserver = TestObserver.create<Optional<SomeEntity>>()

boxStore.runInTx {
    repository.find(123).subscribeWith(testObserver)
}

testObserver.awaitCount(1)
testObserver.assertValueCount(1)

Sometimes, I get a value count of 2 from the original put operation. For completeness, the code of the find() method:

fun find(id: Long): Observable<Optional<SomeEntity>> {
    return Observable.create { emitter ->
        val query = this.boxStore.boxFor(SomeEntity::class)
            .query()
            .equal(SomeEntity_.id, id)
            .build()

        query.subscribe().observer { result ->
            emitter.onNext(result.firstOrNull().toOptional())
        }
    }
}

Assuming I did not misunderstand the docs or misuse the ObjectBox API, it would be great if ObjectBox could offer some method e.g. to block until all notifications triggered by the last transaction have been issued.

Commencez par la séquence runInTx, TestObserver et query.subscribe().observer présentée dans l’issue, puis examinez le comportement des observateurs de données et des transactions d’ObjectBox qu’elle met en jeu. Le travail est terminé lorsqu’il existe un moyen fiable d’attendre les notifications de la transaction précédente, démontré par un test qui reçoit systématiquement l’unique valeur attendue.