Add tests, remove `main` in `WordBoggle`

[Hardvan]

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [x] 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 :white_check_mark:

Project coverage is 65.49%. Comparing base (8d88349) to head (35d03b8).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5782      +/-   ##
============================================
+ Coverage     65.11%   65.49%   +0.38%     
- Complexity     4318     4340      +22     
============================================
  Files           599      599              
  Lines         16747    16742       -5     
  Branches       3213     3212       -1     
============================================
+ Hits          10905    10966      +61     
+ Misses         5397     5332      -65     
+ Partials        445      444       -1     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.