code: def test_forward_mat(self):
      n, d = 4, 5
      test_x = torch.randn(n, d)
      mean = self.create_mean(d)
      self.assertEqual(mean(test_x).shape, torch.Size([n, 2 * d + 1]))
  
file_path: gpytorch/test/means/test_linear_mean_gradgrad.py
imports: import unittest
  import torch
  from gpytorch.means import LinearMeanGradGrad
  from gpytorch.test.base_mean_test_case import BaseMeanTestCase
label_desc: Use image node_id 3 for calling the TestLinearMeanGradGrad obj's underlying member method code with example usage: obj.test_forward_mat() without return types