Slides del workshop "Come si applica l'OCP" all'agile days 2017

1. Come si applica l’Open
Closed Principle
Andrea Francia
@Italian Agile Day 2017
Saturday November, 18th 2017

2. Learning objectives
• How do we do design during Test Driven Development?
• When to do refactor in TDD?
• How much refactor should we do?

3. Why design is
important?

4. Kent Beck. 1999. Extreme Programming Explained: Embrace Change
Legacy Code
Clean Code

5. When Refactor?

6. http://agileinaflash.blogspot.it/2009/02/red-green-refactor.html

7. Refactor last?
• RED
• GREEN
• REFACTOR

8. Refactor first?
• REFACTOR
• RED
• GREEN

9. Refactor first and last
• REFACTOR (to make easier add the new feature)
• RED
• GREEN
• REFACTOR (to remove any duplication)

10. How long to stay in
each phase?

11. http://agileinaflash.blogspot.it/2009/02/red-green-refactor.html

12. The TDD Rhythm:
1. Quickly add a test
2. Run all tests and see the new one fail
3. Make a little change
4. Run all tests and see them all succeed
5. Refactor to remove duplication

13. The TDD Rhythm:
1. Quickly add a test
2. Run all tests and see the new one fail
3. Make a little change
4. Run all tests and see them all succeed
5. Refactor to remove duplication

14. http://agileinaflash.blogspot.it/2009/02/red-green-refactor.html
1-2 minutes
1-2 minutes
take your time

15. The Open/Closed
Principle

16. The “O” in SOLID
• Single Responsibility Principle (SRP)
• Open/Closed Principle (OCP)
• Liskov substitution Principle (LSP)
• Interface Segregation Principle (ISP)
• Dependency Inversion Principle (DIP)

17. The Open/Closed Principle
• You should be able to extend the behavior of a
system without having to modify that system.
https://8thlight.com/blog/uncle-bob/2014/05/12/TheOpenClosedPrinciple.html

18. Open and Closed
Open => we can add behavior just adding new pieces
Closed => we don’t need change old pieces(*)
(*) (no change => no test change, no deploy needed, no
cascading changes )

19. Examples

20. Language libraries
List<Integer> list = ...;
// standard sort
Collections.sort(list);
printAll(list);
// sorting with a specific comparator
Collections.sort(list, new PronounceComparator());
printAll(list);

22. Hexagonal Architecture

23. How to learn to apply
OCP?

24. Kata (repetition)

25. OCP Kata
Open-Closed Principle Kata: http://matteo.vaccari.name/blog/archives/293

26. When do we refactor?
Starting code base Changes implemented
red == code changed
(Hopefully) Code cleaned up
Refactor
after
Starting code base Change design to make
room for new feature
Implement feature
Refactor
before
From a slide by Dave Nicolette

27. OCP Kata Rules
1. Write the first failing test

28. OCP Kata Rules
1. Write the first failing test
2. Then write a factory that returns an object, or an
aggregate of objects, that make the test pass.

29. The factory should be limited to
creating objects and linking them
together. No conditionals allowed.

30. OCP Kata Rules
1. Write the first failing test
2. Then write a factory that returns an object, or an
aggregate of objects, that make the test pass.
3. Write the next failing test.

31. OCP Kata Rules
1. Write the first failing test
2. Then write a factory that returns an object, or an
aggregate of objects, that make the test pass.
3. Write the next failing test.
4. Make the test pass by changing the factory and/or
adding a new class and nothing else.

32. OCP Kata Rules
1. Write the first failing test
2. Then write a factory that returns an object, or an
aggregate of objects, that make the test pass.
The factory should be limited to creating objects and
linking them together. No conditionals allowed.
3. Write the next failing test.
4. Make the test pass by changing the factory and/or
adding a new class and nothing else.
You can’t? Then refactor your code until you can!

33. Workshop time

34. The FizzBuzz Game
1, 2, Fizz!, 4, Buzz!, Fizz!, 7,
8, Fizz!, Buzz!, 11, Fizz!, 13,
14, FizzBuzz!, 16, 17, Fizz!...
If the number is a multiple of 3, say “Fizz”
If it is a multiple of 5, say “Buzz”
If it is a multiple of 3 and 5, say “FizzBuzz”
Otherwise, just say the number.

35. Workshop time
• git clone https://github.com/andreafrancia/ocp-kata.git
• cd ocp-kata
• start-up your IntelliJ IDEA