Adds warning when setting same quiz to class multiple times

[sjd210]

Previously on re-submitting an active test, a toast would display a back-end warning "You cannot reassign a test until the due date has passed."

This change makes it fail earlier (on the front-end), displaying red warning text below the "...group(s)" input and disabling the "Set Test" button.

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I am making use of a top-level let as a workaround to stop polling the back-end on every change to the Set Tests modal (while avoiding dreaded React hook nonsense - otherwise useEffect would be lovely here). Since the value only changes on successfully setting a test, it does not need a re-render so this should be fine - however I'm very open to suggestions for another solution.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 36.83%. Comparing base (24b1e2c) to head (328d4fa).
Report is 236 commits behind head on master.

Files with missing lines	Patch %	Lines
...pp/components/elements/modals/QuizSettingModal.tsx	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1071      +/-   ##
==========================================
- Coverage   36.88%   36.83%   -0.06%     
==========================================
  Files         426      426              
  Lines       18803    18872      +69     
  Branches     5568     5582      +14     
==========================================
+ Hits         6936     6952      +16     
- Misses      11828    11881      +53     
  Partials       39       39              

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[mlt47]

This works and the implementation is along the right lines.
However, I believe that the RTK Query hook is actually doing what you want from it by default, so we should be able to simplify the implementation by switch to just using it! :)

[mlt47]

As we have this information (perhaps retrieved in a different way given other comments) it might be useful to alter groupOptions to add " (already assigned)" to the group label in the drop-down so that the user gets a warning even earlier. It is possible that this will look overcrowded in which case there might be an alternative solution that is nicer - I don't know if the component supports disabled options, for example.

[sjd210]

I think this is a good call, and also that it works best with items being disabled in the StyledSelect.

I initially had some issues with disabled items still being focused by default (annoyingly React has been working on a solution to this for a while), but the change to options in styles solves that in the scope of this page, so I'm pretty happy with it all now.