Automated Qt testing framework

I'd be careful at all when thinking about "manual" testing vs "automated" testing in a return-on-investment (ROI) context. It's a form of fallacious thinking when discussing the value of automation (see the "Time Machine" section of that link).

The Time Machine fallacy summed up is this: the only way you can truly determine the ROI of a testing approach is by having a time machine where you can visit the future and see what happened. Since you (most likely) can't do this, ROI estimations should be seen as a heuristic at best, and not some hard rule. Use current information to make an informed decision about a given testing effort is useful to your team or not.

Instead, when it comes to testing, think about which areas of your product need the most attention, and where the largest risks may be. Perhaps it's been identified that end-to-end integration testing might find the most issues with your app. Even if unit testing brings benefits, those benefits may not be worth the associated costs (getting developer buy in, writing and running tests, etc). Likewise, try thinking about benefits/costs instead of advantages/disadvantages for testing.

I would probably just use ssh to the VM. First copy the executable into the VM using ssh (scp or sftp), then execute it again using ssh and read it's output, possibly use ssh again to pull output files (scp/sftp again, though it's easiest to stick with standard output whenever sufficient) and shut down the VM.

The VM needs to have networking enabled for this, but you can easily prevent it from reaching outside world by configuring firewall on the host.

The VM should have it's disk image mounted in copy-on-write mode and the writable part discarded after the shutdown, so all tests run with the same initial state. You can optionally check that the copy-on-write file does not contain changes to any files it is not supposed to contain.