Test it as a member, not only as an administrator. An admin panel can look correct while the actual member journey is still confusing or broken.
Start with sign-in. Create or use a separate UIID and join the network as a normal member. Confirm that the sign-in route works and that the network does not expose information the member did not grant.
Test the complete first-day journey:
Join the network
Receive an email or notification
Complete the profile or alias context
Create a post
Upload an image
Send a message
Find the community rules
Report a problem or contact a moderator
If video is enabled, test more than one format. FFMPEG is required when uploaded video needs to be converted to MP4. Run the built-in debug check and view the result from a second account.
Test outgoing email with a different provider. Do not only send from and to addresses on the same domain. Check the spam folder and confirm that the sender name and domain are correct.
If payments are enabled, make a real test transaction. Confirm the payment, email receipt, access change, renewal or cancellation path before asking a member to pay.
Test from a phone and a computer. A community is often configured on a desktop and used mainly from mobile devices.