Make test setup more strict

pytest.ini

@@ -3,4 +3,8 @@ xfail_strict=true
 markers =
     offline: Offline tests, aka. tests that can be executed without the need of a client
     expensive: Expensive tests, which should be executed sparingly
-addopts = -m "not expensive"
+addopts =
+    --strict-markers
+    -m "not expensive"
+testpaths = tests
+filterwarnings = error