code: def test_factorset_product(self):
      factor_set1 = FactorSet(self.phi1, self.phi2)
      factor_set2 = FactorSet(self.phi3, self.phi4)
      factor_set3 = factor_set2.product(factor_set1, inplace=False)
      self.assertEqual(
          {self.phi1, self.phi2, self.phi3, self.phi4},
          factor_set3.factors,
      )
  
file_path: pgmpy/pgmpy/tests/test_factors/test_FactorSet.py
imports: import unittest
  from pgmpy.factors import FactorSet
  from pgmpy.factors.discrete import DiscreteFactor
label_desc: Use image node_id 4 for calling the TestFactorSet obj's underlying member method code with example usage: obj.test_factorset_product() without return types