I would expect read to return after a failure without a watchdog function being required.
If you have FFMpeg installed then ffplay is a command line application you can just call it as
ffplay rtsp://…
and leave it running.
The point of the test would be to check ffplay which is built against the same version of FFMpeg as OpenCV to see if the OpenCV implementation is buggy.
Installation will depend on your OS, if its linux then just use the package manager if windows you can download from
but you won’t be able to get the same version as is used in OpenCV so the test may be invalid.