It sounds like you are pursuing a rather intriguing testing scenario with regard to a complex legacy application.   I also have experienced that complex and sometimes interlocking inheritance-paths can create situations that are extremely difficult to test with any confidence that the testing scenario that you’re trying to set up actually matches the reality of the application.   Never really found a good way to approach it, and I didn’t think of this.   I’d love to read a Meditation about what you are doing and/or about the issues that you’re dealing with now, someday soon ...