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/