def test_moments(self):

        p = Beta([2, 3])
        u = p._message_to_child()
        self.assertAllClose(u[0],
                            special.psi([2,3]) - special.psi(2+3))
        
        pass
Iterate over the hierarchy under a root dag node, if root is None, will iterate on whole Maya scene
dataset/ETHPy150Open bayespy/bayespy/bayespy/inference/vmp/nodes/tests/test_beta.py/TestBeta.test_moments--crossover with--dataset/ETHPy150Open CountZer0/PipelineConstructionSet/python/maya/site-packages/pymel-1.0.3/pymel/api/allapi.py/MItDag