Issue 7815. __unittest in module globals trims frames from reported stacktraces in unittest.
diff --git a/Lib/unittest/util.py b/Lib/unittest/util.py
index 9ddf879..7d90ddf 100644
--- a/Lib/unittest/util.py
+++ b/Lib/unittest/util.py
@@ -1,5 +1,8 @@
 """Various utility functions."""
 
+__unittest = True
+
+
 def safe_repr(obj):
     try:
         return repr(obj)