Yesterday Google added the ability to edit code inline within both the AMP test and the mobile-friendly test. So you can run the tools on your URLs and then make code changes in the tool's code editor, rerun the test and see the outcome.
Google recently also added this to the rich results test as well.
Here is what it looks like:
Some good news to start your week! 📢 New feature in the Mobile Friendly and AMP Tests: they now support code editing 🎉
— Google Webmasters (@googlewmc) March 25, 2019
Try it out and let us know what you think...https://t.co/Ei6gfMpjjk https://t.co/RKqeVb3HAG pic.twitter.com/GlHE2p7qNg
Forum discussion at Twitter.