Basically two problems on my side.
.moc is not generated for every dialog as I thought. I got confused by name convention. moc_*.cpp are being produced.
However, I had made another stupid error before. Accidently I had placed my test code into the contructor of the testing class and not in the routine testCase1() as required. However, since I had no problems from the being, I did not pay attention to this details. After moving the code to testCase1() also the test returns from my widget are monitored.