diff --git a/testing/acceptance_test.py b/testing/acceptance_test.py
index 39bd2fd77..1342a416e 100644
--- a/testing/acceptance_test.py
+++ b/testing/acceptance_test.py
@@ -677,6 +677,8 @@ class TestInvocationVariants(object):
     def test_cmdline_python_namespace_package(self, testdir, monkeypatch):
         """
         test --pyargs option with namespace packages (#1567)
+
+        Ref: https://packaging.python.org/guides/packaging-namespace-packages/
         """
         monkeypatch.delenv("PYTHONDONTWRITEBYTECODE", raising=False)