Don't raise empty Snapshots on resets (googleapis#3750)

Author: schmidt-sebastian

google-cloud-clients/google-cloud-firestore/src/main/java/com/google/cloud/firestore/Watch.java

@@ -406,7 +406,6 @@ public void run() {
               Preconditions.checkState(stream == null);
 
               current = false;
-              hasPushed = false;
               nextAttempt = backoff.createNextAttempt(nextAttempt);
 
               stream = firestore.streamRequest(Watch.this, firestore.getClient().listenCallable());

google-cloud-clients/google-cloud-firestore/src/test/java/com/google/cloud/firestore/WatchTest.java

@@ -304,6 +304,35 @@ public void queryWatchReopensOnUnexceptedStreamEnd() throws InterruptedException
     awaitQuerySnapshot(new SnapshotDocument(ChangeType.ADDED, "coll/doc", SINGLE_FIELD_MAP));
   }
 
+  @Test
+  public void queryWatchDoesntSendRaiseSnapshotOnReset() throws InterruptedException {
+    // This test is meant to reproduce https://github.com/googleapis/google-cloud-dotnet/issues/2542
+    addQueryListener();
+
+    awaitAddTarget();
+
+    send(addTarget());
+    send(current());
+    send(snapshot());
+
+    awaitQuerySnapshot();
+
+    close();
+    awaitClose();
+    awaitAddTarget();
+
+    send(addTarget());
+    send(current());
+    // This should not raise a snapshot, since nothing has changed since the last snapshot.
+    send(snapshot());
+
+    send(doc("coll/doc", SINGLE_FIELD_PROTO));
+    send(snapshot());
+
+    // Verify that we only receveived one snapshot.
+    awaitQuerySnapshot(new SnapshotDocument(ChangeType.ADDED, "coll/doc", SINGLE_FIELD_MAP));
+  }
+
   @Test
   public void queryWatchDoesntReopenInactiveStream() throws InterruptedException {
     addQueryListener();