Sometimes this might be caused by the fact that some other module is using the same tracing api (sys.settrace) as debugger, for instance Coverage.py. The solution would be to go to your Rub/Debug Configurations and add --no-cov flag to the Additional Arguments.
Alternatively you might want to delete all --cov in pytest settings (i.e. pytest.ini) or run tests with --no-cov flag, i.e.
pytest test.py --no-cov
It might be also caused by a bad filename, e.g. your file/directory has special characters or spaces in it. Try removing them or changing to e.g. underscore (_).