code: def test_basic():
      a = {"x": 1}
      b = {"y": (inc, "x")}
      layers = {"a": a, "b": b}
      dependencies = {"a": set(), "b": {"a"}}
      hg = HighLevelGraph(layers, dependencies)
  
      assert dict(hg) == {"x": 1, "y": (inc, "x")}
      assert all(
          isinstance(layer, Layer) for layer in hg.layers.values()
      )
  
imports: from __future__ import annotations
  import os
  import threading
  import xml.etree.ElementTree
  from collections.abc import Set
  from concurrent.futures import ThreadPoolExecutor
  import pytest
  import dask
  from dask.blockwise import Blockwise, blockwise_token
  from dask.highlevelgraph import HighLevelGraph, Layer, MaterializedLayer, to_graphviz
  from dask.utils_test import inc
label_desc: Use image node_id 2 for calling a global function with example usage: test_basic() without return types