properly run pytest + cov in the tox env

tox.ini

@@ -17,7 +17,7 @@ deps =
     pytest-cov
 commands =
     flake8
-    python -m pytest
+    pytest --cov={envsitepackagesdir}/incorporealcms/
 
 # whitelist commands we need
 whitelist_externals = ln
@@ -39,13 +39,14 @@ max-complexity = 5
 
 [pytest]
 python_files = tests.py test_*.py
-addopts = --cov --cov-report=term --cov-report=term-missing
+addopts = --cov-report=term --cov-report=term-missing
 
 [coverage:run]
 branch = True
 omit =
-    .tox/*
-    setup.py
-    tests/*
-    versioneer.py
-    incorporealcms/_version.py
+    **/_version.py
+
+[coverage:paths]
+source =
+    ./
+    .tox/**/site-packages/