code: def test_top_len():
      x = da.ones(10, chunks=(5,))
      y = x[:, None] * x[None, :]
  
      d = y.dask.layers[y.name]
      assert len(d) == 4
  
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 8 for calling a global function with example usage: test_top_len() without return types