Search for their username in Snapchat
Check whether their profile still appears in your friends list
Open the chat and see if their Snap score is visible
Try sending them a Snap or message
Look for the Add Friend button on their profile
Check whether your saved chats with them still show normally
See if their story is no longer visible to you
Compare their profile from another account if available
Check whether you can still view their Bitmoji or profile details
Notice if snaps to them stay pending for a long time