Ideally for normal testing of an enable component GuiTestsAssistant is not needed. In some cases where layout needs to take place it is usually enough to draw the Component in memory using an agg graphics context.

Please also note that testing in travis ci takes place in xvfb which could also be a factor (although, I do not think it is related to these failures).

Let me have a look, I can add a couple of test methods to get you started, you can then augment the tests since you know exactly how the component should behave.