Swift Mock Objects: How to Avoid Fragile Tests


I’ve written about my experience of going to try! Swift Tokyo 2017. Now thanks to the video and transcript provided by Realm, I can also share the talk I gave: “Making Mock Objects More Useful”.

Speaking at try! Swift Tokyo on Swift Mock Objects

I start by showing the basics of how to make a Swift mock object by hand. But this easily leads to fragile tests because the assertions are overspecified. We need ways to make tests more malleable, with mocks that are more flexible.

To learn more, see the Realm video. (There’s a written transcript as well.)

Playback speed: Native English speakers may want to increase the playback speed of the video. Because there was simultaneous interpreting, I spoke very slowly, with unusually crisp enunciation. So I was happy when an attendee tweeted in Japanese, “Thanks to the slow speaking style, I could listen without the interpreter for the first time!”

Equality assertions can be too strong

One of my points in the talk is to avoid overusing equality. This is something I’ve addressed before, outside of Swift mock objects. See Let’s Stop Overusing Swift Equatables in Unit Tests

Swift mock objects sample code

When I kept referring to my own sample code for my day job, that gave me a good feeling. If this talk was useful for my own work, I knew it would help others, too. I still check it to remind myself how to write mock objects in Swift!

Do you have any questions about mock objects in Swift? Please share in the comments below.

About the Author Jon Reid

When I was a kid, programming was fun. But working in Silicon Valley, I saw poor code lead to fear, with real human costs. Searching for ways to make life better, I learned about Design Patterns, Refactoring, and Test Driven Development (TDD). Programming became fun again! I've now been doing TDD in Apple environments for 17 years. I'm committed to software crafting as a discipline, with the hope of raising us all to greater effectiveness and joy.

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