Trying to create an api for allowing a list of validators, deferred or n...

...ot.
Please don't import the package at testcase module scope.  Move this code inside a helper method, e.g.

    def _makeDummyDeferredValidateor(self):
        from colander import deferred
        def _validator(node, kw):
            return DummyValidator(kw..get('message', 'Deferred'))
        return deferred(_validator)