08-kata-dependency-breaking.md

% Dependency Breaking Kata % Week 8: Practical Session % Advanced Software Engineering

Learning Objectives

• Practice breaking dependencies using adapters and seams
• Refactor legacy code for testability
• Safely introduce new interfaces

Kata Instructions

Work in pairs to break dependencies in the following code.

C++ Starting Point

class EmailSender {
public:
    void send(const std::string& to, const std::string& body) {
        // Directly uses SMTP library
        SmtpClient smtp;
        smtp.connect("smtp.company.com");
        smtp.sendMail(to, body);
        smtp.disconnect();
    }
};

Python Starting Point

class EmailSender:
    def send(self, to, body):
        # Directly uses SMTP library
        smtp = SmtpClient()
        smtp.connect("smtp.company.com")
        smtp.send_mail(to, body)
        smtp.disconnect()

Tasks

1. Identify Hard Dependencies (15 min)

   • List all direct dependencies in the code
   • Discuss why they make testing difficult

2. Introduce Adapters (25 min)

   • Refactor to use an interface or protocol for the SMTP client
   • Allow injection of a mock or test double

3. Create Seams (30 min)

   • Identify and implement seams for testing
   • Write tests using the new seams/adapters

4. Review and Discuss (20 min)

   • Share your refactoring and tests with another pair
   • Discuss trade-offs and risks

Success Criteria

• Dependencies broken via adapters or seams
• Code is testable with mocks or stubs
• Minimal changes to legacy logic
• Risks and trade-offs discussed

Notes for Facilitators

• Encourage use of interfaces/protocols
• Focus on testability and minimal change
• Discuss real-world applications of these techniques

Follow-up

Prepare for next week's session on:

• Large-scale refactoring
• Managing technical debt
• Strategic improvement planning