adds test_get_factors and test_get_factor_nodes in FactorGraph
adds test_get_factors and test_get_factor_nodes in FactorGraph

jhonatanoliveira/pgmpy,kris-singh/pgmpy,ankurankan/pgmpy,jhonatanoliveira/pgmpy,pgmpy/pgmpy,kris-singh/pgmpy,abinashpanda/pgmpy,khalibartan/pgmpy,ankurankan/pgmpy,khalibartan/pgmpy,pgmpy/pgmpy,abinashpanda/pgmpy,sandeepkrjha/pgmpy,liquidmetal/pgmpy,anaviltripathi/pgmpy,anaviltripathi/pgmpy,sandeepkrjha/pgmpy,liquidmetal/pgmpy