move specialized dir implementations into __dir__ methods (closes #12166)
diff --git a/Lib/test/test_descrtut.py b/Lib/test/test_descrtut.py
index c3355b9..f495e18 100644
--- a/Lib/test/test_descrtut.py
+++ b/Lib/test/test_descrtut.py
@@ -170,6 +170,7 @@
      '__contains__',
      '__delattr__',
      '__delitem__',
+     '__dir__',
      '__doc__',
      '__eq__',
      '__format__',