In reply to avpchandra:
You cannot override a class in the middle chain of inheritance.
One option is to rename test_A to test_A_base, then insert a new class into the chain called test_A that is extended from test_A_base.
If that doesn’t work for you, you’ll have to explain more about what you’re trying to accomplish. There might be other ways of organizing your classes. For example, see the links on this post.