But it is about the thing that's doing. A test is designed with assumptions and knowledge about the thing under test. That two systems perform the same on a tes

But it is about the thing that's doing. A test is designed with assumptions and knowledge about the thing under test. That two systems perform the same on a test doesn't necessarily mean that they will perform the same out of band, so unless the test is exactingly and comprehensively covering the totality of desired behavior/functionality, two fundamentally very different systems may best be tested with two different tests.