code: def test_exists():
      tracker = metrics_tracking.MetricsTracker()
      tracker.register("new_metric", direction="max")
      assert tracker.exists("new_metric")
      assert not tracker.exists("another_metric")
  
imports: import random
  import numpy
  import pytest
  from keras_tuner.backend.keras import losses
  from keras_tuner.backend.keras import metrics
  from keras_tuner.engine import metrics_tracking
label_desc: Use image node_id 3 for calling a global function with example usage: test_exists() without return types