public void addMessageEnvelope(IncomingMessageEnvelope envelope) throws IOException, InterruptedException {
    put(systemStreamPartition, envelope);
    setIsAtHead(systemStreamPartition, true);
  }
A mock SystemConsumer that pretends to be a coordinator stream. The mock will
take all configs given to it, and put them into the coordinator stream's
SystemStreamPartition. This is useful in cases where config needs to be
quickly passed from a unit test into the JobCoordinator.
samza-core/src/test/java/org/apache/samza/coordinator/stream/MockCoordinatorStreamWrappedConsumer.java