For type tox environment use self-check package instead of the test file

tox.ini

@@ -22,7 +22,7 @@ commands = python runtests.py lint {posargs}
 [testenv:type]
 description = type check ourselves
 basepython = python3.6
-commands = python runtests.py testselfcheck -p '-n0' -p '-v'
+commands = python runtests.py self-check -p '-n0' -p '-v'
 
 [testenv:docs]
 description = invoke sphinx-build to build the HTML docs