Here’s a simple guide to avoid new bugs when working with existing code:

1. Use Version Control

  • Create a new branch (e.g., git checkout -b fix/login-bug) before making changes.
  • This keeps the main code safe while you test your fixes.

2. Understand the Code First

  • Read the code carefully. Ask: What does this do? Why was it written this way?
  • Add comments or notes if parts are unclear (but don’t change anything yet).

3. Write Tests First

  • If tests already exist, run them to confirm current behavior.

  • Write unit tests (e.g., with xUnit/NUnit) for the code you’re fixing. Example:

     [Test]  
 public void CalculateTotal_ValidInput_ReturnsCorrectValue()  
 {  
     var result = Calculator.CalculateTotal(100, 0.2);  
     Assert.AreEqual(120, result);  
 }

  • Tests act as a safety net to catch unintended side effects.

4. Make Small Changes

  • Break big tasks into tiny steps (e.g., fix one bug at a time).
  • Test after every small change to catch issues early.

5. Use Tools to Spot Problems

  • Static analyzers (like Roslyn or ReSharper) highlight potential errors.

  • Enable warnings as errors in your project:

       
   true

6. Refactor Safely

  • Use your IDE’s tools (e.g., Visual Studio’s Rename or Extract Method) to avoid manual errors.
  • Follow SOLID principles (e.g., split large classes into smaller ones).

7. Test Again After Changes

  • Re-run all tests (old and new) to ensure nothing broke.
  • Test manually if automated tests don’t cover everything.

8. Review Code with Your Team

  • Ask a teammate to review your changes. Fresh eyes spot mistakes faster.

9. Update Documentation

  • If your change affects how the code works, update comments, READMEs, or wikis.

10. Monitor After Deployment

  • Use logging (e.g., Serilog) or monitoring tools (e.g., Application Insights) to catch issues in production.

Golden Rule:

Always ask, “Could this change break something else?”

Test early, test often, and keep changes small and clear. 🚀