          dimensions = (800, 600)
          f_display.set_display_dimensions(dimensions)
          assert f_display._display_dims == dimensions
  
      @pytest.mark.skip(reason="Headless tkinter will error")
      @pytest.mark.parametrize("columns, face_size", _PARAMS, ids=_IDS)
      def test_update_tk_image(self,
                               columns: int,
                               face_size: int,
                               mocker: pytest_mock.MockerFixture) -> None:
 
</s> remove         # TODO find out how we can test this on a headless system
        # Launching tk.Tk() will result in an error because a display is not found
 </s> add  </s> remove           pip install flake8 pylint mypy pytest pytest-mock wheel
 </s> add           pip install flake8 pylint mypy pytest pytest-mock pytest-xvfb wheel
          dimensions = (800, 600)
          f_display.set_display_dimensions(dimensions)
          assert f_display._display_dims == dimensions
  

      @pytest.mark.parametrize("columns, face_size", _PARAMS, ids=_IDS)
      def test_update_tk_image(self,
                               columns: int,
                               face_size: int,
                               mocker: pytest_mock.MockerFixture) -> None:
keep keep keep keep replace keep keep keep keep keep
 unit test updates
  - Add XVFB (virtual display)
  - Re-activate viewer gui test 
tests/tools/preview/viewer_test.py