code: def test_diff_head(tmp_dir, scm, dvc, exp_stage):
      results = dvc.experiments.run(
          exp_stage.addressing, params=["foo=2"]
      )
      exp = first(results)
  
      assert dvc.experiments.diff(a_rev="HEAD", b_rev=exp) == {
          "params": {
              "params.yaml": {"foo": {"diff": 1, "old": 1, "new": 2}}
          },
          "metrics": {
              "metrics.yaml": {"foo": {"diff": 1, "old": 1, "new": 2}}
          },
      }
  
label_desc: Use image node_id 2 for calling a global function with example usage: test_diff_head(tmp_dir, scm, dvc, exp_stage) without return types