def METHOD_NAME(self):
    ''' Test that the decorate_img method is available on a TileServer instance '''
    img_src1 = ImageSource(Image.new('RGBA', (100, 100)))
    self.called = False
    env = make_wsgi_env('', extra_environ={'mapproxy.decorate_img': self.set_called_callback})
    img_src2 = self.tile_server.decorate_img(
        img_src1, 'tms', ['layer1'],
        env, self.query_extent
    )
    assert self.called == True