Situation

Usually you run tox like this:

tox -e py36

That works, all fine. However, it runs the complete test suite. If you work on a single test function, it is currently not possible to run this alone. You always have to run the complete test suite.

Proposed Solution

I would propose the following small patch to introduce the posargs argument:

diff --git c/tox.ini i/tox.ini
index e172f8a..f7b1b2e 100644
--- c/tox.ini
+++ i/tox.ini
@@ -5,7 +5,7 @@ envlist =
     pypy
 
 [testenv]
-commands = py.test
+commands = py.test {posargs:}

This makes it possible to run tox only for the test function test_should_bump_major:

tox -e py36 test_semver.py::test_should_bump_major

With this single patch, it is even possible to use it for the setup.py script:

python3 setup.py test -a "-e py36 test_semver.py::test_should_bump_major"