Hey there! Let's break down why your Tampermonkey script isn't auto-updating. First, let's start with the script header you shared—notice the incomplete @grant directive at the end? That's a common culprit. Here's your formatted header for reference:

// ==UserScript==
// @name Test script
// @description testing auto-update
// @namespace http://tampermonkey.net/
// @author newbie
// @version 1.0.0
// @updateURL https://github.com/mygithubaccount/test/raw/master/test.user.js
// @downloadURL https://github.com/mygithubaccount/test/raw/master/test.user.js
// @match http://awebsite.com/*
// @run-at document-end
// @grant GM_getResourceText
// @grant GM_addStyle
// @grant GM_xmlhttpRequest
// @grant G...  <!-- This line is truncated and invalid -->
// ==/UserScript==

Here are the key fixes and checks to get auto-updates working:

• Fix the incomplete @grant line: Tampermonkey will skip update checks if it encounters invalid metadata. Either finish writing the full grant name (e.g., GM_setValue if that's what you intended) or delete the truncated line entirely if it's a typo.
• Ensure version numbering is correct: Tampermonkey only updates to scripts with a higher version number than the one installed. If your GitHub-hosted script still uses 1.0.0, increment it (e.g., 1.0.1) to trigger the update.
• Validate your update URLs manually: Copy the @updateURL into your browser and confirm it loads the raw script file without errors (no 404s or permission blocks). Double-check that the repo path and filename are spelled correctly.
• Check Tampermonkey's update settings: Open Tampermonkey's dashboard, go to Settings, and verify:
  • The Auto-update interval isn't set to "Never"
  • Check for updates is enabled
  • Your browser's privacy settings aren't blocking requests to the update source (disable strict ad-blockers or third-party request blockers temporarily to test)
• Trigger a manual update first: Sometimes the auto-update system needs a kickstart. In Tampermonkey's script list, click the update icon next to your "Test script" to pull the latest version manually. Once this works, auto-updates should run on your configured interval.

内容的提问来源于stack exchange，提问作者newbie