TEMP: harden/check

Author: blueyed

src/_pytest/nodes.py

@@ -436,6 +436,7 @@ def gethookproxy(self, fspath):
         from _pytest.python import Package
 
         if not isinstance(self, (Session, Package)):
+            assert isinstance(self, File), self
             # Prevent making it "more public" with the move to the base class.
             raise AttributeError()