We test in proto area not in site-packages.

--- pytest-mock-3.14.0/tox.ini.orig
+++ pytest-mock-3.14.0/tox.ini
@@ -9,7 +9,7 @@
     pytest-asyncio
     pytest6: pytest==6.2.5
 commands =
-    coverage run --append --source={envsitepackagesdir}/pytest_mock -m pytest tests
+    coverage run --append --source=pytest_mock -m pytest tests
 
 [testenv:norewrite]
 commands =