code: def test_custom_objective(self):
      self.cpu_test_bm.run_custom_objective("gpu_hist")
  
file_path: xgboost/tests/python-gpu/test_gpu_basic_models.py
imports: import os
  import sys
  import numpy
  import pytest
  import xgboost
  from xgboost import testing
  import test_basic_models
  import test_callback
label_desc: Use image node_id 2 for calling the TestGPUBasicModels obj's underlying member method code with example usage: obj.test_custom_objective() without return types