diff --git a/unittests/baseplatformtests.py b/unittests/baseplatformtests.py
index b3572df76..251c15d35 100644
--- a/unittests/baseplatformtests.py
+++ b/unittests/baseplatformtests.py
@@ -45,6 +45,11 @@ from run_tests import (
 )
 
 
+# magic attribute used by unittest.result.TestResult._is_relevant_tb_level
+# This causes tracebacks to hide these internal implementation details,
+# e.g. for assertXXX helpers.
+__unittest = True
+
 class BasePlatformTests(TestCase):
     prefix = '/usr'
     libdir = 'lib'