there's another feature

src/allmydata/test/common.py

@@ -853,6 +853,8 @@ class _TestCaseMixin(object):
       test (including setUp and tearDown messages).
     * trial-compatible mktemp method
     * unittest2-compatible assertRaises helper
+    * Automatic cleanup of tempfile.tempdir mutation (pervasive through the
+      Tahoe-LAFS test suite).
     """
     def setUp(self):
         # Restore the original temporary directory.  Node ``init_tempdir``