Thank you for your comments, guys. Yes, I am aware some examples are visible in SmartConsole, but let me explain why I think we need safe testing sites anyway:
1- For malicious or content-sensitive categories, we would prefer not to visit the actual web pages. For example, SmartConsole suggests xvideos.com for the Pornography category (do I really need to browse to an actual pornography site to check if my policy is correctly configured?), and no examples are provided for the Spyware / Malicious Sites category, at least in my SmartConsole version (so how do I check it?).
2- For non-malicious categories, some of the examples do not exist anymore (e.g., anonymizer.com), and most of them use only HTTPS currently, and we would like to check the policies before deploying HTTPS inspection.