[CocoaHeads Tricity] Andrzej Dąbrowski - Dependency injection and testable architecture in Swift apps
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The document discusses the challenges of testing apps in Swift and proposes strategies such as using service locators and dependency injection to improve testability. The author critiques the limitations of mocking frameworks and emphasizes the need for libraries that provide stubs for Apple APIs. Ultimately, the document highlights two third-party libraries, Typhoon and Swinject, as potential solutions for dependency injection in Swift development.
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[CocoaHeads Tricity] Andrzej Dąbrowski - Dependency injection and testable architecture in Swift apps
- 1. Testable apps in Swift Andrzej Dąbrowski andrzej@amplituda.io amplituda.io
- 3. – Our Beloved Client “I have a start-up, I need an app, previous team sucked so I’d like you to continue develop the project”
- 4. Great! Let’s look at the code.
- 5. 1Split code to independent single-purpose services. (no tests without that, sorry)
- 6. 2Write couple of tests.
- 8. Public API
- 9. Why should I make a wrapper around CLLocationManager?
- 10. • seamlessly manages permissions • smoothens out beacon power fluctuations • doesn’t require all listeners to duplicate single beacon filtering code and leaving beacon logic • enable / disable listening • saves energy (takes care of switching between monitoring/ranging automatically) • takes care of background ranging (☠☠☠) • it’s listeners actually don’t have to care about anything, only implement code on beacon events.
- 11. BeaconManager uses another services/APIs • CLLocationManager for permissions and background ranging (updating location) • Logger (sends critical logs to back-end) • Data • SyncManager • NSNotificationCenter
- 13. BeaconManager is critical service to test
- 15. Objective-C dynamic runtime allows us easily change implementation of classes / methods. OCMock!
- 16. Can I do this in Swift? Hmm…
- 18. There are smart people around who claim differently: http://nshipster.com/swift-objc- runtime/ IMVHO, not the best option.
- 19. Where is Swift going? Will there ever be runtime access in Swift?
- 20. I have no idea.
- 21. But if Swift is about to be super-fast and super-safe, I wouldn’t count on it.
- 22. Why Obj-C runtime is so great in testing? • Effortless and quick mocks/stubs • No refactoring needed at all. Just jump into writing tests.
- 23. Disadvantages of OCMock way of testing? • No compile-time protection • We can forget to stub some important things • Encourages a bit to write ugly code (inline mocks / stubs) which could create problems with duplication later • No explicit list of dependencies like in dependency injection • Still have to write mocks / stubs :(
- 24. Alternatives?
- 25. Stubbing based on abstraction layer. Service Locator or DI
- 26. How does it work?
- 27. Service Locator
- 31. Advantages of SL • compile-time • quite quick to implement (actually, sharedInstance properties could be overwritten so that they call Service Locator themselves). • Service protocols are a beautiful way to investigate app architecture without going too deep into implementation details
- 32. Disadvantages of SL • We need to complicate architecture (is that really bad thing?) • We can forget to stub some libs • No explicit list of dependencies (like in DI) • Still have to write our stubs :(
- 33. Dependency injection "Dependency Injection" is a 25- dollar term for a 5-cent concept. James Shore
- 34. "Dependency Injection" is a 25-dollar term for a 5-cent concept. James Shore
- 38. We must initialise services and inject properties when app starts.
- 39. We could use some automation for initialising services.
- 40. Advantages of DI • compile-time • explicit list of dependencies (nice app architecture guard) • we won’t forget to stub anything • service protocols are a beautiful way to investigate app architecture without going too deep into implementation details
- 41. Disadvantages of DI • Quite not-so-fast to implement • Architecture gets more complicated (like in SL) • We still need to write stubs
- 42. SL vs. DI • http://www.martinfowler.com/articles/ injection.html • http://bayou.io/draft/ In_Defense_of_Service_Locator.html • rest of the Internet
- 43. Are there any libraries for Dependency Injection?
- 44. Typhoon Swinject
- 45. Typhoon December, 2012 1667 StarsFirst github commit
- 46. Swinject July, 2015 454 StarsFirst github commit
- 47. There’s a single disadvantage of all testing methods.
- 48. No lib with stubs.
- 49. I’d like to test like this
- 50. Why do I have to write mocks/stubs for Apple or 3rd party libs?
- 51. Let’s take a look at modern framework like angular.js
- 52. Which iOS frameworks could be easily stubbed not to duplicate code?
- 53. Summary • method / class swizzling is probably not what you want in Swift • service locator is quickest way to get legacy code tested • typhoon and swinject are 3rd party libs for Swift testing • swinject seems to be nice • unfortunately, there are no libraries which out of the box give developers stubs / mocks for Apple APIs.
- 54. Thank you