code: def forward_vec(self):
      n = 4
      test_x = torch.randn(n)
      mean = self.create_mean(input_size=1)
      self.assertEqual(mean(test_x).shape, torch.Size([4]))
  
file_path: gpytorch/test/means/test_linear_mean.py
imports: import unittest
  import torch
  from gpytorch.means import LinearMean
  from gpytorch.test.base_mean_test_case import BaseMeanTestCase
label_desc: Use image node_id 2 for calling the TestLinearMean obj's underlying member method code with example usage: obj.forward_vec() without return types