Compiled Learning Objectives

Understanding Legacy Code

• Define legacy code and its characteristics
• List common challenges when working with legacy code

Fear and logic

• Define Chesterton’s Fence

Finding things

• Use IDE features to navigate an unfamiliar codebase
• Trace a request flow through an application
• Sketch system architecture

Debugging: Proposing and Discarding Hypotheses

• Apply scientific debugging methodology to legacy code
• Formulate and test hypotheses systematically
• Use browser debugging tools effectively with legacy applications

Capturing behaviour in tests

• Describe a feature in terms of its behaviour
• Write a test that captures the behaviour of a feature

Fixing: Targeted Changes with Test Support

• Make a small, targeted fix to legacy code
• Use tests to verify fixes don’t break existing functionality
• Document fixes and their rationale

Extending: Adding Features the Right Way

• Add new features that respect existing patterns
• Extend legacy code without breaking existing functionality
• Follow the design principles of the original codebase
• Use test-driven development for new features