Test Suite is using GuiToolAssistant as a way to check if toolkit is Qt

[kitchoi]

While I was working on #552, I realized skipping the Qt-specific test case using the skipIf(toolkit_object.toolkit != "qt4", ...) was not enough, I also had to add a skipIf(GuiTestAssistant.__name__ == "Unimplemented", ...).

This suggests that tests that require Qt, e.g. because the test body contain Qt specific code, are skipped relying on the fact that GuiTestAssistant is only implemented for Qt. This is not ideal, because as soon as GuiTestAssistant is implemented for other toolkit (e.g. wx, see #266), these tests will be run erroneously, causing build errors.

[kitchoi]

That was my stupidity: In the case of when the GuiTestAssistant is not implemented, GuiTestAssistant.__init__ is overridden to raise NotImplemenetedError. The test case needs to place GuiTestAssistant after unittest.TestCase in the MRO so that the test loader can still instantiate the test case before it is skipped. Nothing is wrong here. Sorry for the noise.