public void send(IncomingMessageEnvelope envelope) {
    memoryManager.put(envelope.getSystemStreamPartition(), envelope);
  }
Populates the IME to the ssp configured, this gives user more control to set up Test environment partition.
The offset in the envelope needs to adhere to a rule that for messages in the same system stream partition the
offset needs to start at 0 for the first and be monotonically increasing for the following messages.
If not the {@link InMemoryManager#put(SystemStreamPartition, IncomingMessageEnvelope)} will fail.

Note: Please DO NOT use this in production use cases, this is only meant to set-up more flexible tests.
This function is not thread safe.
@param envelope incoming message envelope
samza-core/src/main/java/org/apache/samza/system/inmemory/InMemorySystemProducer.java