[Solved] How can you test a Kafka Streams topology that aggregates counts per key using TopologyTestDriver? — Ans: Pipe multiple records with same keys and verify output topic has updated counts | Kafka

Kafka - Advanced Stream Processing

How can you test a Kafka Streams topology that aggregates counts per key using TopologyTestDriver?

APipe multiple records with same keys and verify output topic has updated counts

BPipe one record per key and check output for count 1 only

CUse a real Kafka cluster to test aggregation logic

DTest aggregation by reading input topic after processing

Step-by-Step Solution

Solution:

Step 1: Understand aggregation testing
Aggregation updates counts as multiple records with same key arrive.
Step 2: Test approach
Feeding multiple records with same keys and verifying output counts tests aggregation correctly.
Step 3: Evaluate other options
Single record tests only initial count; real cluster not needed; reading input topic does not verify aggregation.
Final Answer:
Pipe multiple records with same keys and verify output topic has updated counts -> Option A
Quick Check:
Test aggregation by multiple inputs and output counts [OK]

Quick Trick: Aggregate by piping repeated keys and checking output counts [OK]

Common Mistakes:

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How can you test a Kafka Streams topology that aggregates counts per key using TopologyTestDriver?