Test improvement in ReplyingKafkaTemplateTests

[sobychacko]

Improve these tests, so that we don't return the actual headers, but maybe Message<?> and then iterate on the headers externally in the tests.

https://github.com/spring-projects/spring-kafka/blob/main/spring-kafka/src/test/java/org/springframework/kafka/requestreply/ReplyingKafkaTemplateTests.java#L1120

https://github.com/spring-projects/spring-kafka/blob/main/spring-kafka/src/test/java/org/springframework/kafka/requestreply/ReplyingKafkaTemplateTests.java#L1140

These tests were originally added via this commit: 97f482a

[snowykte0426]

Hi! I'd like to work on this issue and have a proposed solution.

Proposed Solution

I suggest refactoring these methods to follow the separation of concerns principle:

1. Simplify Listener Methods

Change the listeners to return Message<?> objects instead of validation error strings:

@KafkaListener(id = CUSTOM_REPLY_HEADER_REQUEST, topics = CUSTOM_REPLY_HEADER_REQUEST)
@SendTo(CUSTOM_REPLY_HEADER_REPLY)
public Message<String> handleCustomReplyHeaderNoReplyPartition(ConsumerRecord<?, String> inputMessage) {
    // Only handle business logic
    return MessageBuilder.withPayload("OK")
            .setHeader("originalPayload", inputMessage.value())
            .build();
}

2. Move Header Validation to Test Methods

Extract header validation logic into the test methods themselves:

@Test
public void testCustomReplyTopicHeaderIsNotDuplicated() throws Exception {
    // ... existing setup code ...
    
    Message<?> resultingMessage = future.get(30, TimeUnit.SECONDS);
    
    // Perform header validation externally in the test method
    validateHeaders(resultingMessage, "OK");
    // Additional test-specific validations can be added here
}

3. Add Reusable Validation Utility

Create a utility method for common header validations:

private void validateHeaders(Message<?> message, String expectedPayload) {
    assertThat(message.getPayload()).isEqualTo(expectedPayload);
    assertThat(message.getHeaders()).containsKey("originalPayload");
    assertThat(message.getHeaders().get("originalPayload")).isEqualTo("expected_message");
}

This approach makes the code more modular and follows better testing practices. The length() utility method can also be removed as it's no longer needed.

Would this approach align with the project's goals? I'm happy to implement this solution and submit a PR if this direction looks good.

[artembilan]

Hi @snowykte0426 !

Sounds about right.
Please, feel free to raise a pull request and we can continue a discussion over there on lines.

[snowykte0426]

Hi @sobychacko, @artembilan

I've implemented the test improvements we discussed and created PR #4031
with the following changes:

• Refactored listener methods to return Message<?> objects focusing
  only on business logic
• Extracted header validation into separate utility methods
  (validateHeaders, validateSuccessfulResponse)
• Updated test methods to use external validation approach for better
  separation of concerns
• Cleaned up verbose comments for more maintainable code

The approach follows what we discussed - moving header validation logic
outside the listeners and making the tests more modular. All existing
tests pass and the custom reply header functionality works as expected.

Please let me know if you'd like any adjustments to the implementation