Dependency Breaking Techniques for Legacy Code
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The document discusses 24 dependency breaking techniques for testing legacy code. Some key techniques include: adapt parameter to break dependencies on parameter classes; break out method object to separate logic into new classes; extract and override methods, factories, and getters to inject test logic; introduce instance delegators and static setters to test static methods; and subclass and override methods to break dependencies in object-oriented languages. The techniques aim to separate dependencies but may reduce readability and introduce errors if misused. Legacy code refactoring is challenging, so imperfect techniques are better than no alternatives.
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Dependency Breaking Techniques for Legacy Code
- 1. Dependency Breaking Techniques Working Effectively with LegacyCode Ver 1.0 아키텍트를 꿈꾸는 사람들 cafe.naver.com/architect1 현수명 soomong.net #soomong
- 2. before after 24 dependency breaking techniques
- 3. 1. Adapt Parameter Interface A’ Method ( A ){ ... } Concrete A’ Concrete A’ for production for test
- 4. When to use? - parameter is difficult to test. - can’t use Extract Interface on a parameter’s class.
- 5. 2. Break Out Method Object Class longMethod A() { … … … New Class A } longMethod () { … … … }
- 6. When to use? - method is too large - use instance data and methods
- 7. 3. Definition Completion Definition for Definition Test Concrete Class Concrete Class
- 8. When to use? - language supplies that can declare a type in on place and define it another. - to break dependencies in procedural language like C.
- 9. 4. Encapsulate Global References Class New Class A Global reference Global reference
- 10. When to use? - to separate dependencies on global references.
- 11. 5. Expose Static Method Class Class Static Method () { … Method () { } … }
- 12. When to use? - trying to test code that can’t be instantiated.
- 13. 6. Extract and Override Call Class Class Class for test Method ( ) { Method ( ) { … … logic call A(); … … } } @Override Method A ( ) { Method A( ) { logic test logic } }
- 14. When to use? - trying to test only single method call.
- 15. 7. Extract and Override Factory Method Class Class Class for test constructor( ) { constructor( ) { … … object = new A() object = call A(); … … } } @Override Factory method A(){ Factory method A(){ return new A() … } }
- 16. When to use? - trying to test code that creates objects in constructor.
- 17. 8. Extract and Override Getter Class Class Class for test constructor( ) { constructor( ) { … … object = New A() object = null; … … } } @Override object Getter Method getA(){ Getter Method getA(){ if A is null … object return new A(); } return A; } getA() getA() Lazy initialize
- 18. When to use? - trying to test code that creates objects in constructor - language doesn’t support virtual function call in a derived class from base class’s constructor
- 19. 9. Extract Implementer Duplicated Class Method A() { Interface Class … } virtual Method A() Method A() { … Method B() { virtual Method B() } … } Method B() { … }
- 20. When to use? - hard to naming the interface
- 21. 10. Extract Interface Interface virtual Method A() Concrete Class Class Method A() { virtual Method B() Method A() { … … } } Method A() { Method B() { … … } }
- 22. When to use? - trying to test code that break dependency
- 23. 11. Introduce Instance Delegator Class Class Class for test Static Method A( ) { Static Method A( ) { … … } } @Override Method A’(){ Method A’(){ Class.A() A(); … } } Class.A() instance.A’() instance.A’()
- 24. When to use? - static method has logic that hard to test - it’s weird - 더 큰 리팩토링의 시작
- 25. 12. Introduce Static Setter Class Class Class for test Static instance Static instance private constructor( ) { protected constructor( ) { } } Static Method getInst(){ Static Method getInst(){ if instance is null if instance is null instance = new Class(); instance = new Class(); return instance; return instance; } } @Override Method setInstance(…) { Method setInstance(…) { instance = … test logic } }
- 26. When to use? - Singleton test - Protected constructor = can subclassing = 구리다 - singleton을 코드로 강제하는 것보다는 팀원들이 모두 이해하는게 더 중요하다?
- 27. 13. Link Substitution Global reference for test Call history Value history Method A() { … } Method A() { record call history record value history … }
- 28. When to use? - to break dependencies in procedural language like C.
- 29. 14. Parameterize Constructor Class Class Class for test constructor( ) { constructor( ) { … this( new A() ); object = new A(); } … } constructor( A ) { constructor( A ) { … … object = A; object = test; … … } }
- 30. When to use? - to separate the object that created in constructor. has dependencies on parameter’s class. but it’s a small concern.
- 31. 15. Parameterize Method Class Class Method( ) { Method( A ) { … … object = new A(); object = A; … … } }
- 32. When to use? -to separate the object that created in method. dependency issue? Extract and Override Factory Method is alternative way.
- 33. 16. Primitivize Parameter Class Class TestClass Method ( ) { Method ( ) { TEST( ) { … … … logic call free function(); call free function(); … … } } } free function( ) { logic }
- 34. When to use? - work to get a class under test is too large. - what the…
- 35. 17. Pull Up Feature New Abstract Class Method A( ) { … } abstract Method B abstract Method C Class Method A( ) { … Class Class for test } Method B( ) { TEST( ) { Method B( ) { … CHECK(A()); … } } } Method C( ) { Method C( ) { … … } }
- 36. When to use? - to test just one method that clustered with other methods.
- 37. 18. Push Down Dependency Abstract Class Class Method A( ) { Method A( ) { … … } } Method B( ) { Method B( ) { … … } } abstract drawUI() Method drawUI( ) { … } New Concrete Class Concrete Class for test Method drawUI( ) { Method drawUI( ) { … // do nothing } }
- 38. When to use? - dependencies are pervasive like drawing UI.
- 39. 19. Replace Function with Function Pointer Method main( ) { Method main( ) { … … A(); *pointer … … } } *Method testA( ) { test logic } Method A( ) { … } *Method A( ) { … }
- 40. When to use? - to break dependencies in procedural language like C. Different points of view - horribly unsafe VS useful tool
- 41. 20. Replace Global Reference with Getter Class Class Class for test Global references A Global references A A getA A getA @Override Getter Method getA() { Getter Method getA() { return A; … } }
- 42. When to use? - separate dependencies on global references
- 43. 21. Subclass and Override Method Class Class private Method A(){ protected Method A(){ … … } } subClass for test @Override protected Method A(){ … }
- 44. When to use? - break dependencies in object-oriented language. Many of the other dependency-breaking techniques are variations on it.
- 45. 22. Supersede Instance Variable Class Class Class for test variable variable constructor( ) { constructor( ) { variable; variable; } } @Override supersedeVariable(A) { supersedeVariable(A) { variable = A; … } }
- 46. When to use? - separate objects that created in constructor. - language disallows overrides of virtual function calls in constructors. Use uncommon prefix : supersede 개발자들이 잘못 사용할지도 모르니 잘 모르는 uncommon 한 단어를 prefix 로 사용하자??
- 47. 23. Template Redefinition generics Method ( A ){ ... } Concrete type Concrete type for production for test
- 48. When to use? - language supplies generics and a way of aliasing types.
- 49. 24. Text Redefinition TestClass Class Class def Method A() def Method A() end … logic … end TEST( ) { … test Class }
- 50. When to use? - break dependencies in interpreted language like Ruby.
- 51. 전체 정리하면서 느낀 점 - 억지스러운 면이 자주 보인다. - dependency 는 깨질지 몰라도 Readability는 더 낮아진다. - 코드가 잘못 사용될 수 있으니 개발자가 더 주의 깊게 살펴봐야 한다. - 아무래도 LegacyCode 와의 싸움이 힘겹긴 한가보다. 이해하자. - 억지스럽고 지저분한 방법일지라도 대안이 없다면 그게 바로 최선의 방법이다. - 원문이 훨씬 보기 쉽다. (번역 X)
- 52. Reference 레거시코드 활용 전략 http://www.yes24.com/24/goods/3092523
- 53. 감사합니다