'If any new-style tasks are found, *only* new-style tasks should load'

def test_should_load_decorated_tasks_only_if_one_is_found(self):

    module = fabfile('decorated_fabfile.py')
    with path_prefix(module):
        (docs, funcs) = load_fabfile(module)
        eq_(len(funcs), 1)
        ok_(('foo' in funcs))
