I started off using QtTest for my app and very, very quickly started running into limitations with it. The two main problems were:
1) My tests run very fast - sufficiently quickly that the overhead of loading an executable, setting up a Q(Core)Application (if needed) etc often dwarfs the running time of the tests themselves! Linking each executable takes up a lot of time, too.
The overhead just kept on increasing as more and more classes were added, and it soon became a problem - one of the goals of unit tests are to have a safety net that runs so fast that it is not a burden at all, and this was rapidly becoming not the case. The solution is to glob multiple test suites into one executable, and while (as shown above) this is mostly do-able, it is not supported and has important limitations.
2) No fixture support - a deal-breaker for me.
So after a while, I switched to Google Test - it is a far more featureful and sophisticated unit testing framework (especially when used with Google Mock) and solves 1) and 2), and moreover, you can still easily use the handy QTestLib features such as QSignalSpy and simulation of GUI events, etc. It was a bit of a pain to switch, but thankfully the project had not advanced too far and many of the changes could be automated.
Personally, I will not be using QtTest over Google Test for future projects - if offers no real advantages that I can see, and has important drawbacks.