code: def test_checkpoint_callback_frequency_setter():
      new_checkpoint_callback = callback.CheckpointCallback()
  
      try:
          new_checkpoint_callback.frequency = "a"
      except:
          new_checkpoint_callback.frequency = 1
  
      assert new_checkpoint_callback.frequency == 1
  
      try:
          new_checkpoint_callback.frequency = -1
      except:
          new_checkpoint_callback.frequency = 1
  
      assert new_checkpoint_callback.frequency == 1
  
file_path: opytimizer/tests/opytimizer/utils/test_callback.py
imports: from opytimark.markers.n_dimensional import Sphere
  from opytimizer.core import function
  from opytimizer.optimizers import swarm
  from opytimizer.opytimizer import Opytimizer
  from opytimizer.spaces import search
  from opytimizer.utils import callback
label_desc: Use image node_id 7 for calling a global function with example usage: test_checkpoint_callback_frequency_setter() without return types