Several tools, that are really, really helpful for lots of tests. I use these all the time, and they are incredibly helpful. 

1. Google speed score: showing how well a page is optimized for speed, and all the details needed what can be further optimized.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
2. Google mobile friendly test: much more tests, including if the page has elements that are blocked that might prevent rendering
   
   
   
   
   
   
3. Chrome dev tools: multitude of test.
   Free training / documentation on Google Dev
   
   
   
   
4. Webpagetest.org: the best way to test how it looks for users in a different country, with many of  the same metrics as other tools
   
   
   
   
   
   
   
   
5.  KeyCdn website speedtest to test from multiple locations globally