KIP-1238 — Multipartition for TopologyTestDriver in Kafka Streams

Discussion StreamsTesting

Extends TopologyTestDriver to support multi-partition topics, enabling unit tests that exercise repartitioning, co-partitioned joins, and other partition-dependent stream processing logic. The driver currently simulates all topics as single-partition, making it impossible to test topologies that rely on repartition semantics without spinning up a full EmbeddedKafkaCluster.

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