As a general remark, I think it wouldn't hurt to write a two-sentence explanation in prose (as a class' JSDoc, or a comment in constructor, whatever) what the particular test case class is doing and why it is needed, introducing the test case to the developer who wants to read the code. 

This holds especially for complex scenarios like this one, with multiple test cases inheriting from the same base test etc. 

I don't want to read and follow the complicated flow of the whole test case and its dependencies to know what the test is supposed to be doing.