Add tests for NodeStack and rework

[lorduke22]

• 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 69.33%. Comparing base (90d20b3) to head (3cd1ce4).
Report is 139 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6009      +/-   ##
============================================
+ Coverage     59.71%   69.33%   +9.61%     
- Complexity     3855     4677     +822     
============================================
  Files           561      624      +63     
  Lines         16017    17137    +1120     
  Branches       3073     3311     +238     
============================================
+ Hits           9565    11882    +2317     
+ Misses         6047     4802    -1245     
- Partials        405      453      +48     

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[siriak]

Looks good, thanks!