diff -r 768234f5c246 Lib/test/support.py
--- a/Lib/test/support.py	Sat Jun 25 15:03:52 2011 +0200
+++ b/Lib/test/support.py	Sat Jun 25 16:48:41 2011 +0200
@@ -1601,8 +1601,31 @@ def patch(test_instance, object_to_patch
             setattr(object_to_patch, attr_name, old_value)
         else:
             delattr(object_to_patch, attr_name)
 
     test_instance.addCleanup(cleanup)
 
     # actually override the attribute
     setattr(object_to_patch, attr_name, new_value)
+
+@contextlib.contextmanager
+def operation_timeout(timeout):
+    """A context manager that raise IOError if the operation didn't finish
+    before the given `timeout`.
+
+    Example:
+       >>> import os, time
+       >>> with operation_timeout(1): time.sleep(5)
+       Traceback (most recent call last):
+         ...
+       IOError: Timeout exceeded!
+       >>> with operation_timeout(1): pass
+
+    """
+    import signal
+    def handler(signum, frame):
+        raise IOError("Timeout exceeded!")
+
+    signal.signal(signal.SIGALRM, handler)
+    signal.alarm(5)
+    yield
+    signal.alarm(0)