Sometimes the error messages displayed by the SCT (Submission correctness test, i.e. the test code that runs to determine whether you pass a checkpoint) are confusing.
Years ago I made a bookmarklet that allows you to view the actual test code. Today I updated it after it was completely broken for years.
To install, drag the link to your browser’s bookmarks bar:
Then you can use it on an exercise page:
Disclaimer
This software is provided without any guarantee whatsoever. In fact, I know it only works for a certain older kind of exercise (among other things, it depends on CCDATA.composer being defined).
The source code is on GitHub, so if you have any improvements, please contribute!