Add comments

src/pip/_internal/commands/list.py

@@ -134,6 +134,10 @@ class ListCommand(Command):
             include_editables=options.include_editable,
         )
 
+        # get_not_required must be called firstly in order to find and
+        # filter out all dependencies correctly. Otherwise a package
+        # can't be identified as requirement because some parent packages
+        # could be filtered out before.
         if options.not_required:
             packages = self.get_not_required(packages, options)
 

tests/functional/test_list.py

@@ -384,7 +384,6 @@ def test_outdated_editables_columns_flag(script, data):
     )
 
 
-@pytest.mark.network
 def test_outdated_not_required_flag(script, data):
     """
     test the behavior of --outdated --not-required flag in the list command