code: def test_precision_matrix(self):
      self.assertEqual(self.phi1._precision_matrix, None)
      np_test.assert_almost_equal(
          self.phi1.precision_matrix,
          np.array(
              [
                  [0.3125, -0.125, 0],
                  [-0.125, 0.5833333, 0.3333333],
                  [0, 0.3333333, 0.3333333],
              ]
          ),
      )
      np_test.assert_almost_equal(
          self.phi1._precision_matrix,
          np.array(
              [
                  [0.3125, -0.125, 0],
                  [-0.125, 0.5833333, 0.3333333],
                  [0, 0.3333333, 0.3333333],
              ]
          ),
      )
  
      self.assertEqual(self.phi2._precision_matrix, None)
      np_test.assert_almost_equal(
          self.phi2.precision_matrix, np.array([[1]])
      )
      np_test.assert_almost_equal(
          self.phi2._precision_matrix, np.array([[1]])
      )
  
imports: import unittest
  import numpy
  import numpy.testing
  from pgmpy.factors.distributions import GaussianDistribution
label_desc: Use image node_id 2 for calling the TestJGDMethods obj's underlying member method code with example usage: obj.test_precision_matrix() without return types