def test_repeat_FixAtoms():
    from ase.build import molecule
    from ase.constraints import FixAtoms

    N = 2

    atoms = molecule('CO2')
    atoms.set_cell((15, 15, 15))

    # Indices method:
    atomsi = atoms.copy()
    atomsi.set_constraint(FixAtoms(indices=[0]))
    atomsi = atomsi.repeat((N, 1, 1))

    atomsiref = atoms.copy().repeat((N, 1, 1))
    atomsiref.set_constraint(FixAtoms(indices=list(range(0, 3 * N, 3))))

    lcatomsi = list(atomsi.constraints[0].index)
    lcatomsiref = list(atomsiref.constraints[0].index)

    assert lcatomsi == lcatomsiref

    # Mask method:
    atomsm = atoms.copy()
    atomsm.set_constraint(FixAtoms(mask=[True, False, False]))
    atomsm = atomsm.repeat((N, 1, 1))

    atomsmref = atoms.copy().repeat((N, 1, 1))
    atomsmref.set_constraint(FixAtoms(mask=[True, False, False] * N))

    lcatomsm = list(atomsm.constraints[0].index)
    lcatomsmref = list(atomsmref.constraints[0].index)

    assert lcatomsm == lcatomsmref
    assert lcatomsm == lcatomsi