Allow to only run unit tests with Tox

tox.ini

@@ -25,6 +25,10 @@ basepython = python3.7
 commands =
     black {posargs} .
 
+[testenv:test]
+commands =
+    pytest {posargs}
+
 [testenv:end-to-end]
 deps = -rtest_requirements.txt
 commands =