https://docs.spring.io/spring-integration/docs/current/reference/html/testing.html
    https://github.com/spring-projects/spring-integration-samples

https://docs.spring.io/spring-integration/docs/current/reference/html/testing.html#assertj-conditions-and-predicates
    Starting with version 5.2,
    the MessagePredicate is introduced to be used in the AssertJ matches() assertion.
    It requires a Message object as an expectation.
    And also ot can be configured with headers to exclude from expectation as well as from actual message to assert.

https://livebook.manning.com/book/spring-integration-in-action/chapter-18/