Issue 7815. __unittest in module globals trims frames from reported stacktraces in unittest.
diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index feae3fa..9495689 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -12,6 +12,9 @@
     strclass, safe_repr, sorted_list_difference, unorderable_list_difference
 )
 
+__unittest = True
+
+
 class SkipTest(Exception):
     """
     Raise this exception in a test to skip it.