Public instance methods should be part of an interface

Public instance methods should always be part of an interface. This decouples dependencies and simplifies mocking them in unit tests.

METHOD /clean/blog_post~publish.

In clean object orientation, having a method public without an interface does not make much sense - with few exceptions such as enumeration classes which will never have an alternative implementation and will never be mocked in test cases.

Interfaces vs. abstract classes describes why this also applies to classes that overwrite inherited methods.