def METHOD_NAME(self, app):
    req = (
        r"/service?LAYERs=mapnik&SERVICE=WMS&FORMAT=image%2Fpng"
        "&REQUEST=GetMap&HEIGHT=200&SRS=EPSG%3A4326"
        "&VERSION=1.1.1&BBOX=-90,-90,0,0&styles="
        "&WIDTH=200&"
    )
    resp = app.get(req)
    data = BytesIO(resp.body)
    img = Image.open(data)
    colors = sorted(img.getcolors(), reverse=True)
    # map bg color + black marker
    assert 39700 < colors[0][0] < 39900, colors[0][0]
    assert colors[0][1] == (255, 0, 0, 255)
    assert 50 < colors[1][0] < 150, colors[1][0]
    assert colors[1][1] == (0, 0, 0, 255)