Install test dependencies for CI

Author: pllim

tox.ini

@@ -19,7 +19,8 @@ deps =
     pytest61: pytest==6.1.*
     pytest62: pytest==6.2.*
     pytestdev: git+https://github.com/pytest-dev/pytest#egg=pytest
-
+extras =
+    test
 commands =
     pip freeze
     pytest {toxinidir}/tests {posargs}