def test_fixatoms():
    """Test Atoms.__delitem__ with FixAtoms constraint."""
    from ase import Atoms
    from ase.constraints import FixAtoms

    for i, j in [(slice(0, -1), None),
                 (slice(0, 1), [0]),
                 (slice(0, None), None),
                 (0, [0]),
                 (1, [0]),
                 (2, [0, 1]),
                 (-1, [0, 1])]:
        a = Atoms('H3')
        a.constraints = FixAtoms(indices=[0, 1])
        del a[i]
        print(i, j, a.constraints)
        if j is None:
            assert len(a.constraints) == 0
        else:
            assert (a.constraints[0].index == j).all()
