human
Here's a good function header given the following:
I wrote the below code

    '\n                Notes:    this    test    is    fairly    messy.    PL    made    some    change    to    how\n                FixedVarDescr    worked.    FixedVarDescr    got    an    added    data_specs\n                field.    But    BGD    itself    was    never    changed    to    obey    this    data_specs.\n                Somehow    these    tests    passed    regardless.    It    looks    like    PL    just    built\n                a    lot    of    machinery    into    the    test    itself    to    make    the    individual\n                callbacks    reformat    data    internally.    This    mechanism    required    the\n                data_specs    field    to    be    present.    Weirdly,    the    theano    functions\n                never    actually    used    any    of    the    data,    so    their    data_specs    should\n                have    just    been    NullSpace    anyway.    IG    deleted    a    lot    of    this    useless\n                code    from    these    tests    but    there    is    still    a    lot    of    weird    stuff    here\n                that    he    has    not    attempted    to    clean    up.\n                '
    rng = np.random.RandomState([2012, 11, 27, 9])
    batch_size = 5
    updates_per_batch = 4
    train_batches = 3
    num_features = 2
    w = rng.randn(num_features)
    def make_dataset(num_batches):
        m = (num_batches * batch_size)
        X = rng.randn(m, num_features)
        y = rng.randn(m, num_features)
        rval = DenseDesignMatrix(X=X, y=y)
        rval.yaml_src = ''
        return rval
    train = make_dataset(train_batches)
    model = SoftmaxModel(num_features)
    unsup_counter = shared(0)
    grad_counter = shared(0)
    called = [False, False, False, False]
    class UnsupervisedCostWithFixedVars(Cost, ):
        def expr(self, model, data, unsup_aux_var=None, **kwargs):
            self.get_data_specs(model)[0].validate(data)
            X = data
            assert (unsup_aux_var is unsup_counter)
   ...

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

def test_fixed_vars():