[#12588] Improve test code coverage of core components

[WayyGood]

PR title: [#12588] Improve test code coverage of core components

(PerQuestionViewResponsesComponent)

Outline of Solution
added testing for some uncovered functions

[WayyGood]

link:
https://app.codecov.io/github/TEAMMATES/teammates/tree/master/src%2Fweb%2Fapp%2Fcomponents%2Fquestion-responses%2Fper-question-view-responses

[github-actions]

Hi @WayyGood, thank you for your interest in contributing to TEAMMATES!
However, your PR does not appear to follow our contribution guidelines:

• Title must start with the issue number the PR is fixing in square brackets, e.g. [#<issue-number>]
• Description must reference the issue number the PR is fixing, e.g. Fixes #<issue-number> (or Part of #<issue-number> if the PR does not address the issue fully)

Please address the above before we proceed to review your PR.

[ziqing26]

Hi @WayyGood, thanks for the PR. Please fix the failed Github actions.