Yeah, but that assumes that when you're designing Foo you want to hard code this test hook into the class. This seems like a bad plan for a number of reasons. Problem here is you need to test Foo after it's been created.
I actually tried to figure out how to add a method modifier from the Foo meta class so it only existed during my test case, but couldn't quite figure how to do that yet...so this was my plan B...but I eventually went to plan C after realizing (thanks Chromatic) I could hijack the accessor to the class name. That turned out to be far simpler :)