Can be tested by developers only: Run the webservice/simpletest unit test: to do it you need to enable xmlrpc protocol + the function in the unit test file (and they also need to be set up in the Moodle admin). You also need to change the token. Then you can play with the moodle_notes_create_notes unit test function even thought the default data should be enough to test all error cases. You can also disable Notes in Advanced Feature to check if an exception is thrown.