Goto admin>setting>users>add a new user Try adding a user with all valid detail but with the following in the username field Space - Expected error Capital case - error {}# - error .@ - No error Empty field - error Use a username that already exists in database make sure an appropriate error message is displayed Search for extendedusernamechars setting and enable it Repeat steps 1-3 this time the only ones that produce error should be 2.2,2.5,2.6 Repeat step 2-3 by registering as normal user to the site (signup) disable extendedusernamechars Repeat step 7 (Now error should be produced as mentioned in step 2) Come to my desk and tell me that you enjoyed the recursive testing instructions!