def acquire(self, volume_node_id, volume_name):
        if volume_node_id == self.node_id:
            return fail(ValueError("Can't acquire already-owned volume"))
        volume = Volume(node_id=volume_node_id, name=volume_name, service=self)
        return volume.change_owner(self.node_id)
Make sure useful error messages are available
dataset/ETHPy150Open ClusterHQ/flocker/flocker/volume/service.py/VolumeService.acquire--crossover with--dataset/ETHPy150Open alecthomas/voluptuous/voluptuous/tests/tests.py/test_nested_multiple_validation_errors