Complementary slide deck for my hands-on coding session on testing and refactoring legacy code. Code can be found here: https://github.com/sandromancuso/trip-service-kata

1. Testing and Refactoring
Legacy Code
Sandro Mancuso
@sandromancuso
craftedsw.blogspot.com

2. What is this session about?

3. Business Requirements
Imagine a social networking website for
travellers
• You need to be logged in to see the content
• You need to be a friend to see someone else’s
trips

4. Legacy Code Rules
• You cannot change production code if not
covered by tests
– Just automated refactorings (via IDEs) are allowed,
if needed to write the test

5. Tips
• Use a code coverage tool
• Commit as often as possible
– Enables you to commit (push) improvements
quickly
– Allows you to roll back (reset) if you get lost
• When refactoring, try to stay in the green for
as long as possible

6. Exercise

7. Working with Legacy Code Tips
Start refactoring from
deepest to shortest
branch
Start testing from
shortest to
deepest branch

8. Trip Service - Problems
<<Singleton>>
UserSession
+getInstance() : UserSession
+getLoggedUser() : User
TripService
+findTripsByUser(User) : List<Trip>
TripDAO
+findTripsByUser(User) : List<Trip>

9. Legacy Code Common Problems
• Hard-wired dependencies
– Create a “seam” to break dependencies
• Extract dependency in a protected method
• In our test, extend the class under test and override the
method with the dependency so you can mock the
result
• Identify feature envy
– Move behaviour out to the appropriate class

10. Exercise

11. Remember
Start refactoring from
deepest to shortest
branch
Start testing from
shortest to
deepest branch

12. Refactoring vs Re-design
• After localised refactoring, consider fixing the
design
• Writing tests for existing code may perpetuate
a bad design

13. Craftsmen at work
• Write readable and maintainable code
– Code must express business rules
• Strive for simplicity
• Know your tools well (i.e. frameworks, shortcuts)
• Work in small and safe increments
– Commit often
• Embrace changes, be brave
• Boy scout rule / No broken windows

14. Thanks
https://github.com/sandromancuso/trip-service-kata
Sandro Mancuso
@sandromancuso
craftedsw.blogspot.com