def test_invalid_scalar_index(adata, index):
    # https://github.com/theislab/anndata/issues/619
    with pytest.raises(IndexError, match=r".*index.* out of range\."):
        _ = adata[index]
def _get(delta, start):
            p = start
            while delta:
                p = p.next
                delta -= 1
            return p.val