def METHOD_NAME(self):
    img_src1 = ImageSource(Image.new('RGBA', (100, 100)))
    env = make_wsgi_env('', extra_environ={})
    img_src2 = self.server.decorate_img(
        img_src1, 'wms.map', ['layer1'],
        env, self.query_extent
    )
    assert isinstance(img_src2, ImageSource)