Since version 4.6.0 pytest skips tests without apparent reason: https://travis-ci.org/Snawoot/postfix-mta-sts-resolver/jobs/540181138

• output of pip list from the virtual environment you are using: HERE
• pytest and operating system versions: pytest 4.6.0 on Ubuntu Xenial @ Travis CI
• minimal example if possible: link above

I can't understand why it happens, so I had to immediately rollback to 4.5.0 and fix this version in dev dependencies.