[WIP] Replace JUnit testing framework with TestNG

[Copilot]

Migration Plan: Replace JUnit with TestNG

• Update pom.xml dependency
  • Remove JUnit 4.13.2 dependency
  • Add TestNG dependency
  • Update maven-surefire-plugin if needed
• Update all test files to use TestNG
  • Replace JUnit imports with TestNG imports
  • Replace @test annotations (org.junit.Test → org.testng.annotations.Test)
  • Replace @before with @BeforeMethod
  • Replace Assert.* with TestNG Assert.*
  • Update TestUtil helper class
• Verify all tests still pass
  • Run mvn test to ensure all tests work with TestNG
• Clean up: ensure no JUnit references remain

Original prompt

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This section details on the original issue you should resolve

<issue_title>[feature] replace JUnit testing with TestNG</issue_title>
<issue_description>need to remove JUnit totally and replace with TestNG: https://github.com/testng-team/testng</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [feature] replace JUnit testing with TestNG #504

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.08%. Comparing base (aa90a03) to head (76e6a24).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #505   +/-   ##
=======================================
  Coverage   68.08%   68.08%           
=======================================
  Files          63       63           
  Lines        3083     3083           
  Branches      574      574           
=======================================
  Hits         2099     2099           
  Misses        801      801           
  Partials      183      183           

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