Add Junit tests for AESEncryption.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 54.72%. Comparing base (f34fe4d) to head (7faa8ac).
Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5597      +/-   ##
============================================
+ Coverage     54.56%   54.72%   +0.16%     
- Complexity     3413     3423      +10     
============================================
  Files           535      536       +1     
  Lines         15383    15406      +23     
  Branches       2935     2937       +2     
============================================
+ Hits           8393     8431      +38     
+ Misses         6637     6620      -17     
- Partials        353      355       +2     

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[siriak]

Looks good, thanks!

[Hardvan]

Thanks!