input: From the given instruction and class definition, how would you write a test case to verify the correctness of the forward pass in the `LinearRegressionModel` class?
output:     
      def test_forward_pass():
          model = LinearRegressionModel(input_size=2, output_size=1)
          x = torch.tensor([[1.0, 2.0], [3.0, 4.0]])
          y_pred = model(x)
          assert y_pred.shape == (2, 1), "Output shape is incorrect"
          assert isinstance(y_pred, torch.Tensor), "Output is not a tensor"
  