Add tests for ConvolutionFFT

[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 66.36%. Comparing base (f1aceea) to head (d98e4e5).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5767      +/-   ##
============================================
+ Coverage     66.21%   66.36%   +0.14%     
- Complexity     4428     4438      +10     
============================================
  Files           606      606              
  Lines         16848    16850       +2     
  Branches       3242     3242              
============================================
+ Hits          11156    11182      +26     
+ Misses         5241     5221      -20     
+ Partials        451      447       -4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[alxkm]

@Hardvan need to resolve branch update issues

[Hardvan]

I have resolved the conflicts @alxkm .