def METHOD_NAME(self) -> None:
    f = ff.parse('s(6,4)|v(int)').assign[0](
            range(6)
            )
    post = pivot_items_to_frame(
            blocks=f._blocks,
            group_fields_iloc=[0],
            group_depth=1,
            data_field_iloc=3,
            func_single=lambda x: str(x) if x % 2 else sum(x),
            frame_cls=Frame,
            name='foo',
            dtype=None,
            index_constructor=Index,
            columns_constructor=Index,
            kind='mergesort',
            )
    self.assertEqual(post.to_pairs(),
            (('foo', ((0, '[129017]'), (1, '[35021]'), (2, 166924), (3, 122246), (4, 197228), (5, '[105269]'))),))