human
Solve the following python programming problem given the following code:
def _test_create_volume_backed_image_with_metadata_from_volume(self, extra_metadata = None) : 
    def _fake_id(x) : 
        return ('%s-%s-%s-%s' % ((x * 8), (x * 4), (x * 4), (x * 12))) 
body = dict (createImage = dict (name = 'snapshot_of_volume_backed')) 
    if extra_metadata : 
        body ['createImage'] ['metadata'] = extra_metadata 
image_service = glance.get_default_image_service () 
    def fake_block_device_mapping_get_all_by_instance(context, inst_id, use_slave = False) : 
        return [fake_block_device.FakeDbBlockDeviceDict ({ 
            'volume_id' : _fake_id ('a'), 
            'source_type' : 'snapshot', 
            'destination_type' : 'volume', 
            'volume_size' : 1, 
            'device_name' : 'vda', 
            'snapshot_id' : 1, 
            'boot_index' : 0, 
            'delete_on_termination' : False, 
            'no_device' : None, 
})] 
self.stub_out ('nova.db.block_device_mapping_get_all_by_instance', <MASK>) 
    instance = fakes.fake_instance_get (image_ref = '', vm_state = vm_states.ACTIVE, root_device_name = '/dev/vda', system_metadata = { 
        'image_test_key1' : 'test_value1', 
        'image_test_key2' : 'test_value2', 
}) 
    self.stub_out ('nova.db.instance_get_by_uuid', instance) 
    self.mox.StubOutWithMock (self.controller.compute_api.compute_rpcapi, 'quiesce_instance') 
    self.controller.compute_api.compute_rpcapi.quiesce_instance (mox.IgnoreArg (), mox.IgnoreArg ()).AndRaise (exception.InstanceQuiesceNotSupported (instance_id = 'fake', reason = 'test')) 
    volume = dict (id = _fake_id ('a'), size = 1, host = 'fake', display_description = 'fake') 
    snapshot = dict (id = _fake_id ('d')) 
    self.mox.StubOutWithMock (self.controller.compute_api, 'volume_api') 
    volume_api = self.controller.compute_api.volume_api 
    volume_api.get (mox.IgnoreArg (), volume ['id']).AndReturn (volume) 
    volume_api.create_snapshot_force (mox.IgnoreArg (), volume ['id'], mox.IgnoreArg (), mox.IgnoreArg ()).AndReturn (snapshot) 
    self.mox.ReplayAll...
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def fake_block_device_mapping_get_all_by_instance(