def test_can_remove_previous_residue(self):
res = Residue(self.atom1, self.atom2, self.atom3)
previous_res = Mock(Residue)
res._previous = previous_res
previous_res._next = res
res.previous = None
self.assertIsNone(res._previous)
self.assertIsNone(previous_res._next)
def test_previous_gets_previous(self):
res = Residue(self.atom1, self.atom2, self.atom3)
res._previous = Mock(Residue)
self.assertIs(res.previous, res._previous)