code: def test_model_type_mapper_custom_callable():
      def custom_loss(y_true, y_pred):
          return y_true - y_pred
  
      LossModelTypeMapper().register_loss(
          custom_loss, ModelType.REGRESSION
      )
      assert (
          LossModelTypeMapper().get_model_type("custom_loss")
          == ModelType.REGRESSION
      )
  
imports: import pytest
  from elephas.utils.model_utils import ModelType, LossModelTypeMapper
label_desc: Use image node_id 3 for calling a global function with example usage: test_model_type_mapper_custom_callable() and returns: unknown