code: def test_variables(self):
      self.assertEqual(self.phi1.variables, self.phi1._variables)
      self.assertEqual(self.phi2.variables, self.phi2._variables)
      self.assertEqual(self.phi3.variables, self.phi3._variables)
  
imports: import unittest
  import numpy
  import numpy.testing
  from scipy.special import beta
  from scipy.stats import multivariate_normal
  from pgmpy.factors.distributions import CustomDistribution
label_desc: Use image node_id 6 for calling the TestCustomDistributionMethods obj's underlying member method code with example usage: obj.test_variables() without return types