test: GCDRecursion

[alxkm]

Added test for GCDRecursion.

• 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 45.68%. Comparing base (07dbc51) to head (30905ee).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5361      +/-   ##
============================================
+ Coverage     45.64%   45.68%   +0.04%     
- Complexity     2840     2846       +6     
============================================
  Files           525      525              
  Lines         15425    15425              
  Branches       2921     2921              
============================================
+ Hits           7040     7047       +7     
+ Misses         8090     8083       -7     
  Partials        295      295              

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