The test has been changed in the default branch by changeset
1b174a117e19.  This change replaces the assertIn by a less restrictive
assertTrue. These changes should also probably be made in 3.2 and 2.7
and hopefully this will fix the problem in 3.2 and 2.7.

The changeset 1b174a117e19 in the default branch is:

diff --git a/Lib/test/test_pdb.py b/Lib/test/test_pdb.py
--- a/Lib/test/test_pdb.py
+++ b/Lib/test/test_pdb.py
@@ -604,6 +604,7 @@
         filename = 'main.py'
         with open(filename, 'w') as f:
             f.write(textwrap.dedent(script))
+        self.addCleanup(support.unlink, filename)
         cmd = [sys.executable, '-m', 'pdb', filename]
         stdout = stderr = None
         with subprocess.Popen(cmd, stdout=subprocess.PIPE,
@@ -660,9 +661,11 @@
         """
         with open('bar.py', 'w') as f:
             f.write(textwrap.dedent(bar))
+        self.addCleanup(support.unlink, 'bar.py')
         stdout, stderr = self.run_pdb(script, commands)
-        self.assertIn('main.py(5)foo()->None', stdout.split('\n')[-3],
-                         'Fail to step into the caller after a return')
+        self.assertTrue(
+            any('main.py(5)foo()->None' in l for l in stdout.splitlines()),
+            'Fail to step into the caller after a return')