human
Solve the following python programming problem given the following code:
@ skip_backend (unsupported = { backends.GCE }, reason = 'The GCE backend does not let you create two volumes with the same dataset id. When this test is run with GCE the test fails to create the extra volume, and we do not test the functionality this test was designed to test.') 
@ require_cluster (2) 
def test_extra_volume(self, cluster) : 
    "
        If an extra volume is created for a dataset, that volume isn't used.

        .. note:
           This test will be flaky if flocker doesn't correctly ignore extra
           volumes that claim to belong to a dataset, since the dataset picked
           will be random.
        " 
    api = get_backend_api (cluster.cluster_uuid) 
    wait_for_dataset = create_dataset (api, cluster) 
    created_volume = [] 
    def create_extra(dataset) : 
        volume = api.create_volume (dataset.dataset_id, size = get_default_volume_size ()) 
        created_volume.append (volume) 
        return dataset 
wait_for_extra_volume = wait_for_dataset.addCallback (create_extra) 
    def move_dataset(dataset) : 
        dataset_moving = cluster.client.move_dataset (UUID (cluster.nodes [1].uuid), dataset.dataset_id) 
        moved_dataset = dataset.set (primary = UUID (cluster.nodes [1].uuid)) 
        dataset_moving.addCallback ((lambda dataset : cluster.wait_for_dataset (moved_dataset))) 
        return dataset_moving 
wait_for_move = wait_for_extra_volume.addCallback (move_dataset) 
    def check_attached(dataset) : 
        blockdevice_id = created_volume [0].blockdevice_id 
        [volume] = [volume for volume in api.list_volumes () if (volume.blockdevice_id == blockdevice_id)] 
        self.assertEqual (volume.attached_to, None) 
return wait_for_move.addCallback (check_attached) 
    return wait_for_dataset 

    
    

    Fix the buggy line: wait_for_dataset = create_dataset (api, cluster)
assistant
#Here is Python program to fix the buggy line: wait_for_dataset = create_dataset (api, cluster)
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wait_for_dataset = create_dataset (self, cluster)