code: def test_env_var_canonical_name(monkeypatch):
      value = 3
      monkeypatch.setenv("DASK_A_B", str(value))
      d = {}
      dask.config.refresh(config=d)
      assert get("a_b", config=d) == value
      assert get("a-b", config=d) == value
  
imports: from __future__ import annotations
  import os
  import site
  import stat
  import sys
  from collections import OrderedDict
  from contextlib import contextmanager
  import pytest
  import yaml
  import dask.config
  from dask.config import _get_paths, canonical_name, collect, collect_env, collect_yaml, config, deserialize, ensure_file, expand_environment_variables, get, merge, pop, refresh, rename, serialize, update, update_defaults
  from dask.utils import tmpfile
label_desc: Use image node_id 29 for calling a global function with example usage: test_env_var_canonical_name(monkeypatch) without return types