code: def test_matrix_linear_operator():
      from deepchem.utils.differentiation_utils import LinearOperator
  
      mat = torch.rand(2, 2)
      linop = LinearOperator.m(mat)
      x = torch.randn(2, 2)
  
      result_mm = linop.mm(x)
      expected_mm = torch.matmul(mat, x)
  
      result_mv = linop.mv(x)
      expected_mv = torch.matmul(mat, x.unsqueeze(-1)).squeeze(-1)
  
      assert torch.allclose(result_mm, expected_mm)
      assert torch.allclose(result_mv, expected_mv)
  
imports: import pytest
label_desc: Use image node_id 20 for calling a global function with example usage: test_matrix_linear_operator() without return types