kafka-streams TopologyTestDriver problem with EXACTLY_ONCE

[Frederic Arno]

Hello,

I can't successfully test my processing application which require 
EXACTLY_ONCE processing guarantee using the new TopologyTestDriver. I 
always get the following exception:
java.lang.IllegalStateException: MockProducer hasn't been initialized 
for transactions

The tests all work fine as soon as I set PROCESSING_GUARANTEE_CONFIG to 
AT_LEAST_ONCE.

Am I doing something wrong?

Kafka developpers can reproduce this by adding:
put(StreamsConfig.PROCESSING_GUARANTEE_CONFIG, StreamsConfig.EXACTLY_ONCE);

to line 88 of TopologyTestDriverTest: 
streams/test-utils/src/test/java/org/apache/kafka/streams/TopologyTestDriverTest.java

Thanks, Fred