The map() returns non-null keys and values and produces the following stream:
[KSTREAM-MAP-0000000001]: A , 1 [KSTREAM-MAP-0000000001]: A , 2 [KSTREAM-MAP-0000000001]: B , 3 The issue arises when the combination of map() and groupByKey().count() is used with ProcessorTopologyTestDriver. I have tried the topology on a local Kafka and got the expected result: input: <"A-1", 1>, <"A-2", 2>, <"B-1", 3> result: <"A":2>, <"B":1>. Thanks, Hamid
