public boolean equals(Object other) {
      if (other instanceof SomeKey) {
        SomeKey otherKey = (SomeKey) other;
        return Index == otherKey.Index && PartitionID == otherKey.PartitionID;
      }
      return false;
    }
helper method to test against a functional index make sure there is no UNDEFINED result
geode-core/src/integrationTest/java/org/apache/geode/cache/query/functional/IndexOnEntrySetJUnitTest.java