code: def testSubKeyStr(self):
      self.assertEqual(
          str(metric_types.SubKey(class_id=1)), "classId:1"
      )
      self.assertEqual(str(metric_types.SubKey(top_k=2)), "topK:2")
      self.assertEqual(str(metric_types.SubKey(k=3)), "k:3")
      self.assertEqual(
          str(metric_types.SubKey(class_id=1, top_k=2)),
          "classId:1 topK:2",
      )
  
file_path: model-analysis/tensorflow_model_analysis/metrics/metric_types_test.py
imports: import tensorflow
  from tensorflow_model_analysis.metrics import metric_types
label_desc: Use image node_id 5 for calling the MetricTypesTest obj's underlying member method code with example usage: obj.testSubKeyStr() without return types