Add Unit Test for Negative Hash Codes in HashTable and Note on TimSort Test Limitations

[Kalkwst]

Description

This PR introduces a new unit test to ensure that our custom HashTable implementation correctly handles keys with negative hash codes. Additionally, it includes a discussion on the challenges and limitations of testing certain aspects of the TimSort algorithm due to their deep integration within the private sections of the codebase.

Key Changes

1. Unit Test for Negative Hash Codes:

   • New Test: Test_NegativeHashKey_ReturnsCorrectValue
     • Purpose: Validates that the HashTable can handle keys that generate negative hash codes, ensuring that the data structure remains robust under such conditions.
     • Implementation: The test creates a NegativeHashKey class that generates negative hash codes, adds a key-value pair to the HashTable, and verifies that the value can be retrieved correctly using the same key.

2. Discussion on TimSort Test Limitations:

   • Private Method: FinalizeMerge(TimChunk<T> left, TimChunk<T> right, int dest)

     • The condition left.Remaining == 0 should theoretically never occur if the TimSort algorithm is functioning correctly. This would imply that the left chunk has been entirely consumed before this method is called, indicating a potential bug in the merge logic or an error in the comparison method that leads to an incorrect merge sequence.
     • Writing tests to cover this scenario, as well as other deep parts of the TimSort implementation, is challenging because these methods are private and tightly coupled with the internal logic of the algorithm. To effectively test these edge cases, significant refactoring would be required to expose these methods or alter the structure of the code, which is disproportionate to the value gained from these minor tests.

   • Note on Coverage: Other uncovered methods in TimSort are also deeply embedded within the call chain, making it difficult to create the conditions necessary to trigger them in a controlled testing environment. Given the complexity and potential for unintended side effects, comprehensive testing of these methods would likely require a broader refactoring effort that extends beyond the scope of this PR.

Future Considerations

• Refactoring for Testability: While it is not addressed in this PR, it may be worth considering a future refactor of the TimSort implementation to make it more testable. This could involve exposing key methods or breaking down complex functions into more testable components.

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• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.97%. Comparing base (351b95b) to head (af9eb69).

Additional details and impacted files

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  Coverage   94.97%   94.97%           
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  Files         237      237           
  Lines       10058    10058           
  Branches     1422     1422           
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  Hits         9553     9553           
  Misses        389      389           
  Partials      116      116           

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[siriak]

Could you then remove the check for left.Remaining == 0 in FinalizeMerge? If it's impossible based on the algorithm, we shouldn't validate it because it's a private method. We can guarantee that it won't be called with 0.

To find test cases for other methods, you can do fuzz testing with random arrays and set a breakpoint in the place you want to test. When the breakpoint is hit, you can see arguments that were passed to tim sort and add a test case with these arguments.

Anyway, this PR looks good and I can merge it as-is. Let me know if I need to merge it in the current state or you want to make Tim sort changes here.