code: def test_get_best_step_value_none():
      tracker = metrics_tracking.MetricsTracker()
      tracker.register("val_loss", "min")
      assert tracker.get_best_step("val_loss") is None
  
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 8 for calling a global function with example usage: test_get_best_step_value_none() without return types