This test relied on significant trailing whitespace in a string literal.

Evil.

Lib/test/test_dis.py

@@ -43,7 +43,12 @@ class DisTests(unittest.TestCase):
         sys.stdout = s
         dis.dis(_f)
         sys.stdout = save_stdout
-        self.assertEqual(dis_f, s.getvalue())
+        got = s.getvalue()
+        # Trim trailing blanks (if any).
+        lines = got.split('\n')
+        lines = [line.rstrip() for line in lines]
+        got = '\n'.join(lines)
+        self.assertEqual(dis_f, got)
 
 def test_main():
     run_unittest(DisTests)