test: LinkedListStackTest

[alxkm]

Added LinkedListStackTest.

• 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 46.23%. Comparing base (844aeaf) to head (6982be3).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5366      +/-   ##
============================================
+ Coverage     46.02%   46.23%   +0.20%     
  Complexity     2864     2864              
============================================
  Files           525      525              
  Lines         15412    15412              
  Branches       2916     2916              
============================================
+ Hits           7094     7125      +31     
+ Misses         8021     7989      -32     
- Partials        297      298       +1     

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