Development: Improve course client test coverage

[pal03377]

Checklist

General

• This is a small issue that I tested locally and was confirmed by another developer on a test server.

Client

• Important: I implemented the changes with a very good performance, prevented too many (unnecessary) REST calls and made sure the UI is responsive, even with large data.
• I followed the coding and design guidelines.
• I added multiple integration tests (Jest) related to the features (with a high test coverage), while following the test guidelines.

Motivation and Context

#6318 decreased the coverage for some files related to courses. We aim for a line coverage of >90% per file, so this should be improved.

Description

This PR adds tests to improve the coverage on the files from #6318.

Steps for Testing

Check that the tests pass and make sense.

Review Progress

Code Review

• Code Review 1
• Code Review 2

Test Coverage

This is the complete table (client only) from #6318 with the updated coverage values. Note that the entries in #6318 apparently were still erroneous in part, so some values here are changed even though this PR does not update the related files.

File	Line %	Confirmation	Improved by this PR
alert.service.ts	91.5%	✅	✅
course-overview.component.ts	90.83%	✅	✅
course-registration.component.ts	93.33%	✅	✅
course-prerequisites-button.component.ts	100%	✅
course-registration-button.component.ts	96.15%	✅
course-registration-detail.component.ts	96.15%	✅

[codecov-commenter]

Codecov Report

Merging #6491 (0c955e9) into develop (c110bac) will increase coverage by 0.02%.
The diff coverage is 90.90%.

❗ Current head 0c955e9 differs from pull request most recent head b37189a. Consider uploading reports for the commit b37189a to get more accurate results

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Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #6491      +/-   ##
=============================================
+ Coverage      80.49%   80.52%   +0.02%     
- Complexity     13121    13149      +28     
=============================================
  Files           2333     2339       +6     
  Lines          89763    89779      +16     
  Branches       13244    13233      -11     
=============================================
+ Hits           72257    72293      +36     
+ Misses          9645     9630      -15     
+ Partials        7861     7856       -5     

Impacted Files	Coverage Δ
...epository/plagiarism/PlagiarismCaseRepository.java	100.00% <ø> (ø)
src/main/webapp/app/entities/exercise.model.ts	76.62% <ø> (ø)
...p/exam/participate/exam-participation.component.ts	67.82% <ø> (-0.19%)	⬇️
...chment-unit-form/attachment-unit-form.component.ts	88.88% <66.66%> (+7.49%)	⬆️
...webapp/app/course/manage/course-storage.service.ts	71.42% <71.42%> (ø)
src/main/webapp/app/overview/courses.component.ts	80.00% <75.00%> (-1.82%)	⬇️
...pp/overview/course-exams/course-exams.component.ts	80.00% <80.00%> (+0.83%)	⬆️
...n/webapp/app/overview/course-overview.component.ts	79.38% <80.00%> (+3.05%)	⬆️
...ebapp/app/shared/constants/score-type.constants.ts	85.71% <85.71%> (ø)
...app/app/course/manage/course-management.service.ts	76.68% <86.66%> (-0.17%)	⬇️
... and 20 more

... and 5 files with indirect coverage changes

Flag	Coverage Δ
client	76.53% <89.85%> (+0.03%)	⬆️
server	84.96% <92.68%> (+<0.01%)	⬆️

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[sven0311]

code looks good 👍

[dearjasmina]

code looks good

[lennart-keller]

Code looks really good.

[JohannesStoehr]

Tests look good to me.
One question, is it possible that the subscriptions never actually return anything/are never called actually? I mean that neither () => {...} nor (error) => {...} is invoked?