[#12588] Improve test code coverage of core components

[skylar-mo]

Fixes #12588

Outline of Solution

I added some unit tests to help improve code coverage for "QuestionEditAnswerForm".

[cedricongjh]

hi @skylar-mo, thank you for your PR, do fix the failing tests before we proceed to review it

also do refer to the guidelines here: https://teammates.github.io/teammates/unit-testing.html for writing unit tests, at a glance it appears that the method name is missing from the test descriptor strings, do add that in, thank you! also there is no need to add the test case in a new describe block, do remove that as well

[weiquu]

Closing due to inactivity