Either can be used independently of the other, or they can be combined to deliver the best features of each. Where the Problems Lie Almost all OO tests need a semi-invasive technique that may introduce its own kind of problems to the testing process. When you run your application tests this way there is the risk that, because the application is not really the same one that you are going to be shipping to customers, you can't really be sure that you've tested the same software the customer gets. Neither of these kinds of test outcome helps build confidence in the application's quality if they occur often. Typically, one must link the application to the special Xt library.
Separate builds introduce another source of potential error.
If the testers' program misses a required feature, the test will succeed incorrectly, but that feature will never have been tried. Realism TT tests support realistic load generation. For example, if you are using the background mode X11 server, X11virtual, you know the load you are imposing is just like a real user's load. Vectored Playback Playback of input to something graphical, e.g. idraw, will be completely accurate. This will be detected as the test goes to the previous location of a UI object and tries to invoke it.