Testability
- 4. Flaw: Constructor does Real Work • It violates the Single Responsibility Principle • Tes7ng Directly is Difficult • Subclassing and Overriding to Test is S7ll Flawed • It Forces Collaborators on You
- 6. Warning Signs • new keyword in a constructor or at field declara<on • Sta<c method calls in a constructor or at field declara<on • Anything more than field assignment in constructors • Adding or using an ini<aliza<on block
- 8. Warning Signs • Object not fully ini<alized a2er the constructor finishes (watch out for ini<alize methods) • Control flow (condi<onal or looping logic) in a constructor • CL does complex object graph construc<on inside a constructor rather than using a factory or builder
- 11. Solu<on Do not create collaborators in your constructor, but pass them in. (Don’t look for things! Ask for things!)
- 12. Flaw: Digging into Collaborators getUserManager().getUser(123).getProfile() .isAdmin() // this is egregiously bad (all you need to know if the user is an admin) context.getCommonDataStore().find(1234) // this is bad
- 13. Warning Signs
- 14. Warning Signs • Objects are passed in but never used directly (only used to get access to other objects) • Law of Demeter viola<on: method call chain walks an object graph with more than one dot (.) • Suspicious names: context, environment, principal, container, or manager
- 19. Warning Signs
- 20. Warning Signs • Adding or using singletons • Adding or using sta<c fields or sta<c methods • Adding or using sta<c ini<aliza<on blocks • Adding or using registries • Adding or using service locators
- 27. Flaw: Class Does Too Much a.k.a. … • Kitchen Sink • Dumping Ground • Class who’s Behavior has too many “AND’s” • First thing’s KIll All The Managers (*See Shakespeare) • God Class • “You can look at anything except for this one class”
- 28. Warning Signs
- 29. Warning Signs • Summing up what the class does includes the word “and” • Class would be challenging for new team members to read and quickly “get it” • Class has fields that are only used in some methods • Class has sta<c methods that only operate on parameters
- 31. It Read