How to use get_blank_screen method in Airtest

...84            # 等待下一次需要获取屏幕时，再进行重连85            LOGGING.debug("mjpegsock is closed")86            self._is_running = False87            self.buf.close()88            return self.get_blank_screen()89    def get_frame(self):90        # 获得单张屏幕截图91        return self.get_frame_from_stream()92    def snapshot(self, ensure_orientation=True, *args, **kwargs):93        """94        Take a screenshot and convert it into a cv2 image object95        获取一张屏幕截图，并转化成cv2的图像对象96        !!! 注意，该方法拿到的截图可能不是队列中最新的，除非一直在消费队列中的图像，否则可能会是过往图像内容，请谨慎使用97        Args:98            ensure_orientation: True or False whether to keep the orientation same as display99        Returns: numpy.ndarray100        """101        screen = self.get_frame_from_stream()102        try:103            screen = aircv.utils.string_2_img(screen)104        except Exception:105            # may be black/locked screen or other reason, print exc for debugging106            traceback.print_exc()107            return None108        if ensure_orientation:109            if self.ori_function:110                display_info = self.ori_function()111                orientation = next(key for key, value in ROTATION_MODE.items() if value == display_info["orientation"])112                screen = aircv.rotate(screen, -orientation, clockwise=False)113        return screen114    def get_blank_screen(self):115        """116        生成一个黑屏图像，在连接失效时代替屏幕画面返回117        Returns:118        """119        if self.ori_function:120            display_info = self.ori_function()121            width, height = display_info['width'], display_info['height']122            if display_info["orientation"] in [90, 270]:123                width, height = height, width124        else:125            width, height = 1080, 1920126        img = numpy.zeros((width, height, 3)).astype('uint8')127        img_string = aircv.utils.img_2_string(img)128        return img_string...

...52            cv2.imshow("test", img)53            c = cv2.waitKey(10)54            time.sleep(0.05)55        cv2.destroyAllWindows()56    def test_get_blank_screen(self):57        img_string = self.mjpeg_server.get_blank_screen()58        img = aircv.utils.string_2_img(img_string)59        aircv.show(img)60    def test_teardown_stream(self):61        self.mjpeg_server.get_frame()62        if self.mjpeg_server.port_forwarding is True:63            self.assertTrue(is_port_open(self.mjpeg_server.ip, self.mjpeg_server.port))64            self.mjpeg_server.teardown_stream()...