`tox` command fails at coverage report

When I ran tox command as described in the document, the following error occured.

report: commands[0]> coverage report
No data to report.
report: exit 1 (0.13 seconds) /home/koyuki/pytest-cov> coverage report pid=112348

[webknjaz]

@koyuki7w that's not enough context. Could you post the full log of tox -vvvvv?