Review feedback

Author: rsgowman

firebase-firestore/src/main/java/com/google/firebase/firestore/model/mutation/ArrayTransformOperation.java

@@ -51,11 +51,12 @@ public FieldValue applyToRemoteDocument(FieldValue previousValue, FieldValue tra
   }
 
   @Override
-  public final boolean equals(Object o) {
+  @SuppressWarnings("EqualsGetClass")  // subtype-sensitive equality is intended.
+  public boolean equals(Object o) {
     if (this == o) {
       return true;
     }
-    if (!(o instanceof ArrayTransformOperation)) {
+    if (o == null || getClass() != o.getClass()) {
       return false;
     }
 

firebase-firestore/src/testUtil/java/com/google/firebase/firestore/testutil/TestUtil.java

@@ -432,7 +432,9 @@ public static PatchMutation patchMutation(
 
     boolean merge = updateMask != null;
 
-    // We sort the fieldMaskPaths to make the order deterministic in tests.
+    // We sort the fieldMaskPaths to make the order deterministic in tests. (Otherwise, when we
+    // flatten a Set to a proto repeated field, we'll end up comparing in iterator order and
+    // possibly consider {foo,bar} != {bar,foo}.)
     SortedSet<FieldPath> fieldMaskPaths = new TreeSet<>(merge ? updateMask : objectMask);
 
     return new PatchMutation(