Issue 7815. __unittest in module globals trims frames from reported stacktraces in unittest.
diff --git a/Lib/unittest/loader.py b/Lib/unittest/loader.py
index 9eede8b..d6c8d84 100644
--- a/Lib/unittest/loader.py
+++ b/Lib/unittest/loader.py
@@ -10,6 +10,8 @@
 
 from . import case, suite
 
+__unittest = True
+
 
 def _CmpToKey(mycmp):
     'Convert a cmp= function into a key= function'