code: def test_cost_withGradients_user_defined_cost(self):
      def f(x):
          return x * x
  
      cost_model = CostModel(f)
      cost, d_cost = cost_model.cost_withGradients(np.array([2, 2]))
  
      self.assertEqual(cost, 4)
      self.assertEqual(d_cost, 4)
  
file_path: GPyOpt/GPyOpt/testing/core_tests/test_cost.py
imports: import unittest
  import numpy
  from GPyOpt.core.task import CostModel
  from GPyOpt.core.task.cost import constant_cost_withGradients
label_desc: Use image node_id 6 for calling the TestCostModel obj's underlying member method code with example usage: obj.test_cost_withGradients_user_defined_cost() and returns: unknown