Swift Testing

Starting Unit testing in Swift


An important part of efficient software development is unit testing. It enables you to check that specific pieces of your code are functioning properly, assisting you in finding and fixing errors early on and ensuring the high quality of your code. In this post, we’ll look at the fundamentals of Swift unit testing and show you how to start using them in your own applications.

Unit testing – what is it?

A type of testing called unit testing focuses on distinct pieces of code, usually at the function level. A unit test puts a particular piece of code through its paces and ensures that it functions as intended.

A testing framework like XCTest, which offers utility functions for authoring and running tests, is generally used to write unit tests. By developing a test class with methods that contain the test prefix, you may write unit tests in Swift.

What makes unit testing so important?

In software development, unit testing is crucial for a number of reasons:

  • Before your code is made available to users, it aids in the early detection and correction of issues. + It gives you peace of mind that your code is functioning properly, enabling you to make updates and changes without fearing that they’ll break something.
  • You can rearrange your code more easily because you are certain that no new defects have been caused by your changes.
  • As it pushes you to consider edge cases and error handling, it helps to ensure that your code is of a high caliber.

How can I begin with Swift unit testing?

You must carry out the following before you can begin unit testing in Swift:

  • Create a target for testing in your Xcode project. All of your test code will be included in this separate target.
  • Utilizing the XCTest framework, create test scenarios. A test case is a collection of connected tests that verify a certain functionality or feature of your code.
  • Execute your tests, then examine the outcomes.

To illustrate how this actually functions, let’s look at an example.

Testing a simple function

Let’s say we have a function that adds two numbers and returns the result, add(x: Int, y: Int) -> Int. In order to make sure that this function is operating properly, we want to create a unit test.

  • Go to the File menu in Xcode and pick New > Target.
  • Click Next after selecting iOS, Test, and Unit Test Case Class.
  • After selecting your test class, click Finish.

The test case can then be written. We’ll build a method in our test class with the test prefix that calls our add function and confirms that it produces the expected result. Here is an example of our test case:

func testAdd() {
    let result = add(x: 2, y: 3)
    XCTAssertEqual(result, 5)

As explained in a previous post, the XCTest framework’s XCTAssertEqual function is a tool that verifies that an expression is equal to the expected value. The test will fail if the expression does not match the predicted value.

The Test button in the top toolbar or the U keyboard shortcut can be used to execute our tests. Our tests will be executed by Xcode, and the results will be shown in the Test Navigator pane.

Guidelines for creating efficient unit tests

Here are some pointers to assist you in creating strong unit tests:

  • Keep the focus of your tests. A single behavior or feature should be tested in each test. *Create independent testing. When creating tests, stay away from relying on the results of other tests or the overall application state.
  • When naming your tests, be thoughtful. This will make it simpler to comprehend each test’s purpose and significance.
  • Make use of many test cases. Make sure you test edge situations and error handling in addition to the happy path.


This post taught us the fundamentals of unit testing in Swift and how to start using them in our own projects. Unit testing is a crucial step in the development process that enables us to make sure that our code is error-free and of the highest quality. Using the XCTest framework, we saw an example of how to set up a testing target in Xcode and create a test case.

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