Google has updated the Mobile-Friendly Test tool adding the ability to test the code. Now webmasters may check their websites before launching them, not after as it was before.
If you find some errors in the code, you can correct them all and repeat the test.
Also, when using the Mobile Friendly and AMP Test tools, users can switch between buttons adding the URL or pasting source code. Previously, you could only enter the actual URL. When testing the source code, results appear in the same format as when checking the URL.
In November 2018 Google updated its tool for evaluating site load speed PageSpeed Insights.