Unit tests should be as free of external dependencies as possible. This means that you want to have full control over everything that happens in your tests. For example, if you're working with a database, you want the database to be empty or in some predefined state before your test starts. You operate on the database during your test and after your test the database can be thrown away. By making your tests not depend on external state, you make sure that your tests are repeatable, can run in parallel and don't depend on one test running before another test....

Swift's new modern testing framework is entirely driven by asynchronous code. This means that all of our test functions are async and that we have to make sure that we perform all of our assertions “synchronously”. This also means that completion handler-based code is not as straightforward to test as code that leverages structured concurrency. In this post, we’ll explore two approaches that can be useful when you’re testing code that uses callbacks or completion handlers in Swift Testing. First, we’ll look at the built-in confirmation method from the Swift Testing framework and why it might not be what you...

In a previous post, I wrote about using the #expect macro to ensure that certain assertions you want to make about your code are true. We looked at testing boolean conditions as well as errors. In this post, I would like to take a look at a macro that goes hand-in-hand with #expect and that is the #require macro. The #require macro is used to ensure that certain conditions in your test are met, and to abort your test if these conditions are not met. The key difference between #expect and #require is that #expect will not cause a failed...

I don't think I've ever heard of a testing library that doesn't have some mechanism to test assertions. An assertion in the context of testing is essentially an assumption that you have about your code that you want to ensure is correct. For example, if I were to write a function that's supposed to add one to any given number, then I would want to assert that if I put 10 into that function I get 11 out of it. A testing library that would not be able to do that is not worth much. And so it should be...

When you subscribe to the practice of test-driven development or just writing tests in general you'll typically find that you're going to be writing lots and lots of tests for pretty much everything in your codebase. This includes testing that varying inputs on the same function or on the same object result in expected behavior. For example, if you have a function that takes user input and you want to make sure that you validate that a user has not entered a number greater than 100 or smaller than 0, you're going to want to test this function with values...

Swift testing is Apple's framework for running unit tests in a modern and more elegant way than it was with XCTest, which came before it. This post is the first one in a series of posts that will help you start using Swift Testing in your projects. In this post, we'll take a look at the following topics: Adding a Swift Testing to an existing project Writing your first Swift test Understanding Swift Testing syntax Let's go ahead and dive right in and see what it takes to add a new Swift test to an existing project. Adding a Swift...

The Swift testing framework is an incredibly useful tool that allows us to write more expressive tests with convenient and modern APIs. This is my first post about Swift Testing, and I’m mainly writing it because I wanted to write about something that I encountered not too long ago when I tried to use Swift testing on a code base where I had both async code as well as older completion handler based code. The async code was very easy to test due to how Swift Testing is designed, and I will be writing more about that in the future....

A question that often comes up when folks get into learning Combine is "how do I test code that uses Combine?". In this week's post, I will briefly explain the basics of testing Combine code. I will assume that you already know the basics of testing and Combine. If you're just getting started with both topics or would like a refresher I can recommend that you take a look at the following resources: My series of posts on testing My series of posts on Combine My Practical Combine book if you want to learn a lot more about Combine, and...

Modern applications often rely on data from a network connection to work as intended. Sometimes they rely heavily on the network and are almost worthless without an internet connection while other apps can function mostly fine without a network connection. What these apps have in common is that they contain code that might be challenging to write tests for. Whenever you write unit tests, you should always strive to make your tests as predictable, reproducible and most importantly independent of external factors as possible. This is a huge difference compared to integration testing where you’d test a certain part of...

In part 1 of this two-part blog post, you’ve learned how to write synchronous unit tests for a login view model. As a reminder, you saw how to implement tests for the following requirements: When both login fields are empty, pressing the login button should trigger an error that informs the user that both fields are mandatory. When one of the two fields is empty, pressing the login button should trigger an error that informs the user that the empty field is mandatory. When the user’s email address does not contain an @ symbol, pressing the login button should trigger...