An aspect of testing Java programs that seems to me fairly neglected is testing conformance to interfaces, and (nearly identically) testing that functionality of abstract classes works properly in all concrete subclasses. Certainly this has been mentioned before, generally under the name Abstract Tests or Contract Tests. Also, the idea seems to me very much in keeping with Behaviour Driven Development (BDD) and the Design by Contract (DbC) philosophy.

TestNG does not explicitly support Contract Tests, as far as I can tell, but it’s fairly easy to make it work using the little trick I describe below.

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