old_contents: #!/usr/bin/python
  
  """ To document. """
  
  from surface_mock import SurfaceMock
  
  class ScreenMock(object):
      """ Mock class for Screen. """
  
      def __init__(self, name):
          """ Default constructor. """
          self.font_manager = None
          self.name = name
  
      def set_font_manager(self, manager):
          """ """
          self.font_manager = manager
      
      def generate_preview():
          """ """
          return SurfaceMock()
new_contents: #!/usr/bin/python
  
  """ To document. """
  
  from surface_mock import SurfaceMock
  
  class ScreenMock(object):
      """ Mock class for Screen. """
  
      def __init__(self, name):
          """ Default constructor. """
          self.font_manager = None
          self.name = name
  
      def set_font_manager(self, manager):
          """ """
          self.font_manager = manager
      
      def generate_preview(self):
          """ """
          return SurfaceMock()
subject: Fix screen_mock#generate_preview()