def wait(n):
    import time
    time.sleep(n)
    return n
Ensures that ``cache_tree_children`` fails with a ``ValueError`` when
dataset/ETHPy150Open ipython/ipython-py3k/IPython/parallel/tests/clienttest.py/wait--crossover with--dataset/ETHPy150Open django-mptt/django-mptt/tests/myapp/tests.py/CacheTreeChildrenTestCase.test_cache_tree_children_with_invalid_ordering