Add tests for SkylineAlgorithm.java

[Hardvan]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.27%. Comparing base (41f767e) to head (ffcfe78).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5556      +/-   ##
============================================
+ Coverage     53.00%   53.27%   +0.26%     
- Complexity     3315     3328      +13     
============================================
  Files           530      530              
  Lines         15356    15356              
  Branches       2926     2926              
============================================
+ Hits           8140     8181      +41     
+ Misses         6881     6837      -44     
- Partials        335      338       +3     

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[siriak]

Looks good, thanks!

[Hardvan]

Thank you!