code: def test_viewer():
      viewer = ImageShow.Viewer()
  
      assert viewer.get_format(None) is None
  
      with pytest.raises(NotImplementedError):
          viewer.get_command(None)
  
file_path: pillow/Tests/test_imageshow.py
imports: from __future__ import annotations
  import pytest
  from PIL import Image, ImageShow
  from .helper import hopper, is_win32, on_ci
label_desc: Use image node_id 6 for calling a global function with example usage: test_viewer() without return types