code: def test_checkpoint_callback():
      new_checkpoint_callback = callback.CheckpointCallback()
  
      assert new_checkpoint_callback.file_path == "checkpoint.pkl"
      assert new_checkpoint_callback.frequency == 0
  
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 5 for calling a global function with example usage: test_checkpoint_callback() without return types