def test_and_combinations(self):
        assert_equal((volA & volB), volume.CVDefinedVolume(op_id, 0.25, 0.5))
        assert_equal((volA & volB)(0.45), True)
        assert_equal((volA & volB)(0.55), False)
        assert_equal((volB & volC), volume.EmptyVolume())
        # go to VolumeCombination if order parameter isn't the same
        assert_equal((volA & volA2),
                     volume.VolumeCombination(volA, volA2,
                                              lambda a, b: a and b,
                                              '{0} and {1}')
                    )