code: def setUp(self):
      self.model = LinearGaussianBayesianNetwork(
          [("x1", "x2"), ("x2", "x3")]
      )
      self.cpd1 = LinearGaussianCPD("x1", [1], 4)
      self.cpd2 = LinearGaussianCPD("x2", [-5, 0.5], 4, ["x1"])
      self.cpd3 = LinearGaussianCPD("x3", [4, -1], 3, ["x2"])
  
file_path: pgmpy/pgmpy/tests/test_models/test_LinearGaussianBayesianNetwork.py
imports: import unittest
  import numpy
  import numpy.testing
  from pgmpy.factors.continuous import LinearGaussianCPD
  from pgmpy.factors.discrete import TabularCPD
  from pgmpy.models import LinearGaussianBayesianNetwork
label_desc: Use image node_id 1 for calling the TestLGBNMethods obj's underlying member method code with example usage: obj.setUp() without return types