'Assert that C{container._enumerants} does not change as a side-effect
of one of its attributes being accessed.
@param container: A L{_ConstantsContainer} subclass which will be
tested.
@param constantName: The name of one of the constants which is an
attribute of C{container}.'

def _initializedOnceTest(self, container, constantName):

    first = container._enumerants
    getattr(container, constantName)
    second = container._enumerants
    self.assertIs(first, second)
