def METHOD_NAME(self, app, base_dir):
    assert base_dir.join("cache.gpkg").check()
    # already created on startup
    self.common_map_req.params.bbox = "-180,0,0,80"
    serv = MockServ(port=42423)
    serv.expects("/tiles/01/000/000/000/000/000/001.png")
    serv.returns(create_tmp_image((256, 256)))
    with serv:
        resp = app.get(self.common_map_req)
        assert resp.content_type == "image/png"
        data = BytesIO(resp.body)
        assert is_png(data)
    # now cached
    resp = app.get(self.common_map_req)
    assert resp.content_type == "image/png"
    data = BytesIO(resp.body)
    assert is_png(data)