'Construct an Xblock with split mongo kvs.'

def get_block_using_split_kvs(self, block_type, block_id, fields, defaults):

    kvs = SplitMongoKVS(definition=Mock(), initial_values=fields, default_values=defaults, parent=None)
    self.field_data = InheritingFieldData(inheritable_names=['inherited'], kvs=kvs)
    block = self.get_a_block(usage_id=self.get_usage_id(block_type, block_id))
    return block
