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 serialize(self, value, display=False):
        lookup = {v: k for k, v in self.levels.items()}
        if value in lookup:
            return encode(lookup[value])
        return ""