Below is a list of my favourite Schema structured data testing tools:

Google structured data testing tool

https://search.google.com/structured-data/testing-tool/u/0/

Before publishing to the web you can test your Schema for any errors. You can either paste a snippet of code or enter the URL for structured already published online.

FAQPage JSON-LD Schema Generator

https://saijogeorge.com/json-ld-schema-generator/faq/

Testsize

testsize.com

Tool to check how your website appears using various screen resolutions including: 240×320 (mobile), 320×480, 640×480, 1024×600, 1280×800, 1280×800, 1280×800 and 1280×800. Using the + or – keys you can zoom in or out to change the resolution in small increments. The space bar allows you to cycle through the standard screen sizes listed above.