docstr: Assign made-up gradient to test custom_gradient.
docstr_tok: ["Assign","made-up","gradient","to","test","custom_gradient","."]
code: def test_custom_gradient_one_vector_var(self):
      """Assign made-up gradient to test custom_gradient."""
  
      def grad_x(x):
          return 6 * x
  
      @gs.autodiff.custom_gradient(grad_x)
      def func(x):
          return gs.sum(x**2)
  
      arg_x = gs.array([1.0, 3.0])
      result_value, result_grad = gs.autodiff.value_and_grad(func)(
          arg_x
      )
  
      expected_value = 10.0
      expected_grad = gs.array([6.0, 18.0])
  
      self.assertAllClose(result_value, expected_value)
      self.assertAllClose(result_grad, expected_grad)
  
imports: import warnings
  import numpy
  import pytest
  import geomstats.backend
  from geomstats.geometry.grassmannian import Grassmannian
  from geomstats.geometry.special_euclidean import SpecialEuclidean
  from geomstats.test.test_case import TestCase, autograd_and_torch_only, autograd_only, np_only
label_desc: Use image node_id 10 for calling the TestAutodiff obj's underlying member method code with example usage: obj.test_custom_gradient_one_vector_var() and returns: unknown, gs