CONTENT_FORMAT_PREFERRED Machine Test: Check MIME types of content with various devices and check that the preferred format is sent or that the format is compatible with the Default Delivery Context.

• 内容格式首选机器测试：用不同设备检查内容的MIME类型，并检查内容是以最佳格式发送的，或内容格式和默认传输对象兼容。