The LMS app sends username not userid:

https://github.com/hypothesis/lms/blob/d6b88fd7e375a4b23899117556b3e39cfe18986b/lms/static/scripts/frontend_apps/components/LMSGrader.js#L36

But the test for ths client code that receives this was sending
userid.

Fix the test to send username, the same as the LMS app does.