Delete useless test because GetSet exists and add some test for GetSetEventManager.

[jenovateurs]

Hello!
Delete tests useless and empty.
Add new tests unit.

• Type: code quality
• Link to issue: Refactor Unit Tests - Add more tests #13655

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Thanks

[codecov]

Codecov Report

Merging #14740 into 4.0.x will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            4.0.x   #14740      +/-   ##
==========================================
+ Coverage   67.97%   67.97%   +<.01%     
==========================================
  Files         483      483              
  Lines      111435   111435              
==========================================
+ Hits        75749    75752       +3     
+ Misses      35686    35683       -3

[ruudboon]

thnx @jenovateurs