Write test assertions that are both comprehensive and maintainable. Ensure all relevant fields and behaviors are validated, while using generic matchers where appropriate to reduce brittleness. **Comprehensive Coverage**: Assert all relevant fields in response objects, not just error codes. For example, when testing fetch responses, verify highWatermark, logStartOffset, and other expected fields: ```scala // Instead of only checking error assertEquals(Errors.NONE, responses(topicIdPartition).error) // Also verify other relevant fields assertEquals(Errors.NONE, responses(topicIdPartition).error) assertEquals(highWatermark, responses(topicIdPartition).highWatermark) assertEquals(leaderLogStartOffset, responses(topicIdPartition).logStartOffset) ``` **Maintainable Assertions**: Use generic matchers like `anyLong()` instead of hardcoded values when the specific value isn't critical to the test logic: ```scala // Instead of brittle specific values verify(coordinator, times(0)).updateLastWrittenOffset(0) verify(coordinator, times(1)).updateLastWrittenOffset(2) verify(coordinator, times(1)).updateLastWrittenOffset(5) // Use generic matchers when appropriate verify(coordinator, times(0)).updateLastWrittenOffset(anyLong()) verify(coordinator, times(3)).updateLastWrittenOffset(anyLong()) ``` This approach ensures tests validate the complete behavior while remaining resilient to implementation changes that don't affect the core functionality being tested.