Pablo, I can see the error in Travis. The difference I can see is that the tests are executed sequentially in coverage run but normal run has tests executing in parallel. Felix and Federico, can you please add the command you use to run the tests?

Sample error build : https://travis-ci.com/github/python/cpython/jobs/396688564#L2022

coverage run but has true in the end thus being always successful

xvfb-run ./venv/bin/python -m coverage run --branch --pylib -m test --fail-env-changed -uall,-cpu -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_multiprocessing_spawn -x test_concurrent_futures || true

Normal run

/home/travis/build/python/cpython/python -u -W default -bb -E -m test -r -w -j 1 -u all -W --slowest --fail-env-changed --timeout=1200 -j4 -uall,-cpu