code: def test_merge_stat():
      # Ensure that `MetricName`s are hashable
      metric_name = MetricName("some_metric")
      stats: Dict[MetricName, Stat] = {
          metric_name: Stat(metric_name).add(1)
      }
      merge_stat(stats, Stat(metric_name).add(1))
  
      assert len(stats) == 1
      assert stats[metric_name].sum == 2
  
imports: from typing import Dict
  from .metric_name import MetricName
  from .statistic import Stat, merge_stat
label_desc: Use image node_id 1 for calling a global function with example usage: test_merge_stat() without return types