How to effectively verify unit test side effect without code generation in Swift — Often we need to unit test code with side-effects that interact with other parts of your system using abstraction — protocols in Swift. There are many techniques to build that abstraction and verify if our code works as expected: stubbing, spying, dummying etc. Previously, I made a deep dive into…

Unit tests and memory leaks — How do you assert that your code doesn’t introduce any unexpected cycles that lead to memory leaks? Do you actually verify weak/strong references in unit tests? …

Build Rules to select a file variant — If you want to configure your iOS/Mac (Swift or Objective-C) build with some alternative variant, there are plenty of different approaches to follow. In general, you can divide them into two clusters: switch it in runtime (e.g. parsing Info.plist) or compile-time (leveraging Swift Compilation Conditions/Preprocessor Macro or define new target)…

How to quickly write unit test stub in Swift without code generation — Often we need to unit test a code with side-effects that interact with other parts of your system by abstraction— protocols in Swift. There are many ways to verify if it works as expected: stubbing, spying, dummying etc. …

We all love protocol extensions, one of the most powerful element of protocol oriented programming (POP) in Swift. Despite their unquestionable benefits, there are some rare cases where you should avoid them. …

How to handle errors in iOS apps — There isn’t a lot of articles about error handling in the iOS ecosystem, even this seems to be a non easy and substantial component of each app. Today, I wish to tackle this problem and present my solution towards less disruptive error handling in the iOS app. Initial state To ensure that…

Practicing TDD using Xcode IDE can be a bit disruptive. Every time you introduce a small change in the implementation or test file, Xcode rebuilds entire project (fortunately using incremental build) and installs the app on a simulator. Depending which project configuration you have, it may take from a few…

How to test non-called completion handler scenario Testing completion-handler API happy path scenario is really simple with XCTestExpectation. Things get complicated if your test case has to verify whether given handler was not called. It is still straightforward if it’s called synchronously after some other event that you emulate. But…

Safety over simplicity — Swift language was designed with a focus on “safe by default” approach (do not confuse with “safe by design” — Swift does not prevents you from doing dangerous actions but only encourages for good practices). One of such incentive is a great support for sum and product data types, enum…