add comment

Author: smacke

src/_pytest/fixtures.py

@@ -1735,6 +1735,7 @@ def parsefactories(
             return
 
         module_types = (types.ModuleType,)
+        # support IPython's DummyMod if the module containing it has been imported
         if (DummyMod := getattr(sys.modules.get("IPython.core.interactiveshell"), "DummyMod", None)) is not None:
             module_types += (DummyMod,)
         # Avoid accessing `@property` (and other descriptors) when iterating fixtures.