TaskSideInputHandler build() {
      return spy(new TaskSideInputHandler(taskName,
          taskMode,
          storeBaseDir,
          stores,
          storeToSSPs,
          storeToProcessor,
          systemAdmins,
          streamMetadataCache,
          new CountDownLatch(1),
          clock));
    }
This test is for cases, when calls to systemAdmin (e.g., KafkaSystemAdmin's) get-stream-metadata method return null.
samza-core/src/test/java/org/apache/samza/storage/TestTaskSideInputHandler.java