test: `CircleLinkedListTest`

[alxkm]

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Added tests.

• [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 49.66%. Comparing base (a9bc7c2) to head (14a204d).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5422      +/-   ##
============================================
+ Coverage     49.34%   49.66%   +0.31%     
- Complexity     3067     3080      +13     
============================================
  Files           524      524              
  Lines         15204    15195       -9     
  Branches       2890     2890              
============================================
+ Hits           7503     7547      +44     
+ Misses         7389     7336      -53     
  Partials        312      312              

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