Fix/bubble sort negative numbers

[P-Ved]

Perfect 👍
Below is a clear, complete, and easy-to-read description that includes EVERYTHING you did with my help, written in simple language so any user or maintainer can quickly understand it.

You can directly copy-paste this as your PR description.

---

📄 Pull Request Description (Simple & Complete)

What changes did I make?

In this pull request, I improved the unit tests for multiple algorithms to make them more reliable, clearer, and better at handling edge cases.

Detailed summary of changes

• Bubble Sort

  • Improved test readability and assertion order
  • Added tests for empty arrays, null input, negative numbers, mixed strings, and stability of sorting
  • Made tests more consistent with JUnit 5 best practices

• Binary Search

  • Added tests for null input and empty arrays
  • Improved coverage for single-element and large arrays
  • Cleaned up test structure and naming for better readability

• Factorial

  • Improved tests for negative input validation
  • Verified correct results for small inputs
  • Added coverage for large factorial values to ensure correctness

• GCD (Greatest Common Divisor)

  • Updated tests to correctly handle negative numbers using mathematical rules
  • Added clear tests for zero values, arrays, multiple arguments, and large numbers
  • Improved overall test clarity and consistency

• Fibonacci Number Check

  • Added tests for zero and negative numbers
  • Improved readability using clear test names
  • Ensured correct identification of Fibonacci and non-Fibonacci numbers

Why are these changes important?

• Improves test coverage and catches edge cases
• Makes the codebase safer and more reliable
• Helps prevent future regressions
• Makes the project easier to understand for beginners and contributors

Did I change any algorithm logic?

❌ No.
All changes are test-only. The algorithm implementations remain unchanged.

---