code: def test_metrics_diff_active_branch_unchanged(
      tmp_dir, scm, dvc, run_copy_metrics
  ):
      def _gen(val):
          metrics = {"a": {"b": {"c": val, "d": 1, "e": str(val)}}}
          (tmp_dir / "m_temp.yaml").dump(metrics)
          run_copy_metrics(
              "m_temp.yaml",
              "m.yaml",
              name="copy-metric",
              metrics=["m.yaml"],
              commit=str(val),
          )
  
      _gen(1)
      _gen(2)
      _gen(1)
  
      assert dvc.metrics.diff(a_rev=tmp_dir.scm.active_branch()) == {}
  
imports: import json
  from os.path import join
  import pytest
  from dvc.cli import main
  from dvc.utils import relpath
  from dvc.utils.serialize import JSONFileCorruptedError
label_desc: Use image node_id 15 for calling a global function with example usage: test_metrics_diff_active_branch_unchanged(tmp_dir, scm, dvc, run_copy_metrics) without return types