Manual:MakeTestEdits.php

Details
makeTestEdits.php maintenance script allows a developer to made random edits for testing. This is a very helpful feature for those who run test wiki and want to create some random pages to testing a new version or patch.

Common error
This means, you are not giving the valid username of an existing user on wiki. If given username contains spaces then please look Tip 1 above.
 * No such user exists.