code: def test_get_timeline_plot(
      trial_states_list: list[TrialState],
  ) -> None:
      study = _create_study(trial_states_list)
      fig = plot_timeline(study)
      fig.get_figure().savefig(BytesIO())
  
imports: from __future__ import annotations
  from io import BytesIO
  import pytest
  from optuna.trial import TrialState
  from optuna.visualization.matplotlib._timeline import plot_timeline
  from tests.visualization_tests.test_timeline import _create_study
label_desc: Use image node_id 1 for calling a global function with example usage: test_get_timeline_plot(trial_states_list) without return types