Issue 7815. __unittest in module globals trims frames from reported stacktraces in unittest.
diff --git a/Lib/unittest/runner.py b/Lib/unittest/runner.py
index 2fe01f6..f9e1995 100644
--- a/Lib/unittest/runner.py
+++ b/Lib/unittest/runner.py
@@ -5,6 +5,8 @@
 
 from . import result
 
+__unittest = True
+
 
 class _WritelnDecorator(object):
     """Used to decorate file-like objects with a handy 'writeln' method"""