code: def test_index_subs():
      assert index_subs(tuple("ij"), {"i": "j", "j": "i"}) == tuple(
          "ji"
      )
  
imports: from __future__ import annotations
  import collections
  from operator import add
  import numpy
  import pytest
  import dask
  import dask.array
  from dask.array.utils import assert_eq
  from dask.blockwise import _BLOCKWISE_DEFAULT_PREFIX, Blockwise, _unique_dep, index_subs, optimize_blockwise, rewrite_blockwise
  from dask.highlevelgraph import HighLevelGraph
  from dask.utils_test import dec, hlg_layer_topological, inc
label_desc: Use image node_id 2 for calling a global function with example usage: test_index_subs() without return types