def test_atoms_get_duplicates():
    from ase import Atoms
    from ase.geometry import get_duplicate_atoms

    at = Atoms('H5', positions=[[0., 0., 0.],
                                [1., 0., 0.],
                                [1.01, 0, 0],
                                [3, 2.2, 5.2],
                                [0.1, -0.01, 0.1]])

    dups = get_duplicate_atoms(at)
    assert all((dups == [[1, 2]]).tolist()) is True

    dups = get_duplicate_atoms(at, cutoff=0.2)
    assert all((dups == [[0, 4], [1, 2]]).tolist()) is True

    get_duplicate_atoms(at, delete=True)
    assert len(at) == 4

    at = Atoms('H3', positions=[[0., 0., 0.],
                                [1., 0., 0.],
                                [3, 2.2, 5.2]])

    # test if it works if no duplicates are detected.
    get_duplicate_atoms(at, delete=True)
    dups = get_duplicate_atoms(at)

    assert dups.size == 0