What's a common flaky-test cause when testing Kafka consumers, and how is it usually fixed?

Asserting immediately after producing a test message, before the consumer (running on its own poll thread) has actually had a chance to process it — a race condition that passes sometimes and fails other times depending on timing. The fix is using a polling `Awaitility`-style assertion (retry the assertion for up to N seconds) instead of a single immediate check.