'When not otherwise initialized, the attribute evaluates to a
``_SyncToThreadedAsyncAPIAdapter`` using the global reactor, the global
reactor\'s thread pool, and the value of ``block_device_api``.'

def test_default(self):

    threadpool = reactor.getThreadPool()
    api = UnusableAPI()
    deployer = BlockDeviceDeployer(hostname=u'192.0.2.1', node_uuid=uuid4(), block_device_api=api)
    self.assertEqual(_SyncToThreadedAsyncAPIAdapter(_reactor=reactor, _threadpool=threadpool, _sync=api), deployer.async_block_device_api)
