human
I wrote the below code

    def check_aggregator(kv, key, key_list):
        num_devs = 4
        devs = [mx.Context('cpu', i) for i in range(num_devs)]
        vals = [mx.nd.ones(shape, d) for d in devs]
        kv.push(key, vals)
        kv.pull(key, out=vals)
        for v in vals:
            check_diff_to_scalar(v, num_devs)
        vals = ([[(mx.nd.ones(shape, d) * 2.0) for d in devs]] * len(key_list))
        kv.push(key_list, vals)
        kv.pull(key_list, out=vals)
        for vv in vals:
            for v in vv:
                check_diff_to_scalar(v, (num_devs * 2.0))
    check_aggregator(init_kv(), 3, keys)
    check_aggregator(init_kv_with_str(), 'a', str_keys)

What's a good function header?
assistant
#Here's a good function header.

def test_aggregator():