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Exploring iOS Unit Testing

A Comprehensive Guide to Efficiently Writing and Implementing iOS Unit Tests

July 31, 2023
Kazuaki MatsuoKazuaki Matsuo
Kazuaki Matsuo


As a business owner, you know the importance of testing your products before launch. With the introduction of iOS unit testing, the app testing process has been made much easier. iOS unit testing is software testing that involves testing individual units of source code for iOS apps. Using iOS swift unit testing and iOS app unit testing, you can identify bugs quickly and make sure that your app functions properly and meets the required standards.

This blog will teach us about iOS unit testing and how it can help you develop and launch high-quality apps.

Check out: A comprehensive guide to unit testing

Why is iOS Unit Testing Important?

iOS app unit testing enables developers to test individual code units, such as classes and functions, to ensure they function correctly. Automating the process of catching errors early in development cycles by running simple yet meaningful tests – developers can save time and money while providing customers with better-quality apps.

Unit tests for iOS can be written in either Swift or Objective-C and are typically executed using an automated testing framework XCTest. The framework provides the necessary tools for developers to create, run, and evaluate their unit tests. Tests can range from simple 'yes/no' questions to more complex ones requiring the developer to specify conditions to verify if a piece of code is working correctly.

What are the Advantages of iOS Unit Testing?

  • Increased reliability: Unit tests help identify and remove code bugs as they are written, resulting in a more reliable software product.
  • Improved maintainability: Unit tests create an additional layer of documentation that describes how the code works, which makes it easier to maintain the code in the future.
  • Reduced development time: Unit tests can be run automatically, which helps to identify potential problems before they become an issue in the development process.
  • Increased code coverage: Unit tests help to ensure that all of the code is tested, which helps to prevent new bugs from being introduced in the future and clarify unknown behavior.
  • Improved quality assurance: Unit tests are a form of automated quality assurance, which helps to ensure that the code is functioning as expected.
  • Increased confidence: Knowing that the code is being tested and is functioning as expected can give developers and stakeholders added confidence in the product.

iOS unit testing has become a must-have for distributed projects or those relying heavily on remote collaboration tools like GitHub or Bitbucket. Standardized tests guarantee that all members involved produce consistent outcomes regardless of location - expediting debugging efforts and speeding up the development process.

Which are the Frameworks Available for iOS Unit Testing?

Let's discuss the unit testing fundamentals in iOS.

  • XCTest is a testing framework developed by Apple that enables developers to write tests in Swift or Objective-C. Swift project also develops its XCTest by extracting common parts from Xcode. It provides support for both UI and unit tests, making it a versatile choice for iOS testing needs. XCTest has various features, including debugging tools, performance measurements, and more.

Exploring the Popular UI Testing Frameworks: A Comprehensive Guide to Seamless Test Automation

In addition to XCTest, which is primarily used for unit testing, there are various UI testing frameworks available for automating tests that focus on the user interface of mobile apps. These UI testing frameworks are specifically designed to simulate user interactions and validate the behavior of the app's graphical elements.

  • One popular UI testing framework is XCTest itself, which provides an XCTest User Interface Tests API for iOS app UI testing. With XCTest User Interface Tests, you can write UI tests in Swift or Objective-C to interact with the app's UI elements, perform actions like tapping buttons, entering text into text fields, and verifying expected UI states. XCTest UI Testing integrates well with Xcode and is commonly used by iOS developers for UI automation.
  • Appium is an open-source mobile automation framework developed by Microsoft that supports multiple platforms such as iOS, Android, and Windows Phone. It provides an easy way for developers to run automated tests without learning scripting languages like Java or Python. Appium also has built-in support for object recognition using element locators such as XPath or ID selectors, which makes writing tests much simpler.
  • Calabash is another popular open-source framework for automating mobile applications on iOS and Android devices. It uses Cucumber syntax, which allows developers to write human-readable scenarios, which are then automatically converted into tests by the framework itself. The main benefit of Calabash is its intuitive feature set which makes it simple to use even if you have no experience with automated testing before.
  • EarlGrey is Google's open-source testing platform for iOS that is designed to provide a similar experience in Espresso, which is specifically for Android development. The 1.0 version was based on XCTest Unit Testing Bundles, but the 2.0 version is XCTest User Interface Tests basis. 

When choosing an iOS UI test framework, it's essential to consider the type of application you're developing and any cost factors. Appium might be better if cross-platform compatibility is needed, while XCTest might be more suitable for native app testing. Whatever framework you choose should provide visibility into how individual units behave within your application.

Learn more: A Comprehensive Guide to Choosing Between Appium and XCTest (UI) for iOS App Testing

What Aspects Can Be Tested with Unit Testing?

Below are some of the aspects of unit testing that can be tested:

  • Functionality: Unit tests can verify that a given code unit is performing as expected and producing the output for a given input.
  • Dependency: Unit tests can be used to verify that a given unit of code is not dependent on any other components.
  • Code Coverage: Unit tests can measure how much of the code is being tested and identify any gaps in coverage.
  • Performance: Unit tests can be used to measure the performance of individual units of code, as well as identify any inefficiencies in the code.
  • Security: Unit tests can verify that a given code unit is secure and not vulnerable to any potential security issues.
  • Quality Assurance: Unit tests can ensure that a given code unit meets the quality standards set by the development team.
  • Error Handling: Unit tests can be used to verify that a given unit of code is appropriately handling errors and that it is not failing unexpectedly.

How Does HeadSpin Enable Developers to Seamlessly Conduct iOS Unit Testing?

Starting with iOS unit testing can initially seem daunting, but it doesn't have to be. You can quickly set up your environment and write effective tests with the right tools and knowledge.

HeadSpin offers a comprehensive solution for developers looking to get the most out of their testing efforts. With HeadSpin's platform, developers can test their apps across multiple devices, quickly identify any issues with their code, and get real-time feedback on their performance. This allows them to make informed decisions about their code and develop reliable applications without waiting for manual testing cycles to complete.

Here are the HeadSpin capabilities that provide seamless execution of iOS app unit testing:

  1. Device Selection - HeadSpin's Platform allows developers to select the device they choose for testing, providing access to various mobile and tablet devices. This enables developers to test their applications on multiple versions of iOS and other operating systems and different hardware configurations.
  1. Automation - HeadSpin's Platform also provides automation capabilities, allowing developers to set up test scripts that run regularly. iOS swift automation testing can save time and resources, as developers don't have to manually run tests every time they make changes to their codebase.
  1. Performance Monitoring - HeadSpin's Platform provides real-time performance monitoring, allowing developers to view their applications' performance across different devices. This helps developers identify issues with their code quickly and efficiently, as well as track their performances.
  1. Data Science-driven Test Reports - HeadSpin's Platform also provides detailed test reports generated through AI, which provide a comprehensive overview of the results of each test run. These reports can help developers quickly identify any issues with their code or performance and track their tests' progress over time. 
Read: Performance Testing Challenges and their solutions

Exploring the Process of Writing iOS Unit Tests on the HeadSpin Platform

Writing unit tests for iOS applications is essential to ensuring code quality and stability. This section outlines the steps for writing iOS unit tests and provides some HeadSpin-specific code examples.

Step 1: Create a Test with XCTest Framework

Target To separate your unit tests from the main project code, creating a separate test target is the best practice. Follow these steps to make a test target:

a) In Xcode, go to the "File" menu and select "New"> "Target..."

b) Choose the "iOS Unit Testing Bundle" template.

c) Enter a name for the test target and ensure it's added to your project.

Also read: Android vs iOS App Performance Testing

Step 2: Write Unit Tests

Now that your test target is set up, it's time to write unit tests.

Here's an example of a unit test for a hypothetical Calculator class:

import XCTest
@testable import YourProjectName
final class calculatorTests: XCTestCase {
	var calculator: Calculator!
	override func setUp() {
    	calculator = Calculator()
	override func tearDown() {
    	calculator = nil
	func testAddition() {
    	let result = calculator.add(2, 3)
    	XCTAssertEqual(result, 5, "Addition result is incorrect")
	func testSubtraction() {
    	let result = calculator.subtract(5, 3)
    	XCTAssertEqual(result, 2, "Subtraction result is incorrect")

In this example, we import the main project's module (@testable import YourProjectName) to access the Calculator class. We define two test methods: testAddition and testSubtraction. We use the Calculator instance in each test method and assert that the result matches our expectations using XCTAssertEqual. This test case is simple, so the instance creation for Calculator can be in each test case, but this example test code explains how to use setUp and tearDown to prepare/cleanup the test environment outside the exact test code.

Step 3: Run Unit Tests

To execute the unit tests, follow these steps:

a) Select your test target in the Xcode toolbar's scheme selector.

b) Press the "Test" button (or use the shortcut Cmd+U).

c) Xcode will run all the unit tests while displaying the results in the Test Navigator and the console.

Check: Ensuring Successful Software Development Through Emphasis on Software Testers’ Needs

Step 4: Analyze Test Coverage

Xcode provides a comprehensive test coverage analysis feature to help you understand the percentage of code covered by your unit tests. After running your tests, follow these steps to view the test coverage:

a) Go to the "Report Navigator" in Xcode (Cmd+9).

b) Select the latest test run report.

c) In the report details, navigate to the "Coverage" tab.

d) Here, you can explore the coverage percentages and view which parts of your code are covered or missed by the unit tests.

Step 5: Run tests on the HeadSpin device

HeadSpin provides network analytics. Unit test code can have exact network communication as well to check the exact connection. Of course, it depends on your test design if you mock everything or not.

  1. Attach to an iOS device on the HeadSpin platform over HS connect
  2. Select the device as the test target via the Xcode
  3. Start a capture session via Session API
  4. Run tests against the device
  5. Stop the capture session

Please make sure the provisioning profile is set properly to run the tests on the real device.

Summing Up

iOS unit testing is an essential part of any development project. It helps developers efficiently create bug-free code while providing insights into their apps' performances. With many frameworks and tools, developers can easily set up their environment and start writing tests quickly.

For developers looking to take their testing efforts to the next level, HeadSpin’s AI-driven Platform provides a comprehensive testing solution that allows them to identify any code issues and get real-time performance feedback quickly.

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Q1. What is the difference between UI and unit testing in iOS?

Ans: Unit testing in iOS focuses on providing rapid and regular feedback to developers, helping them gain confidence in the correctness of their code. It validates individual code units in isolation. On the other hand, UI testing in iOS validates the entire application from an end user's perspective. It ensures that the final product performs as users expect, testing the application as a whole.

Q2. What are the steps for utilizing Xcode for iOS testing?

Ans: To utilize Xcode for iOS testing, follow these steps:

  1. Create an Apple ID: Agree to Apple's service policies and create an Apple ID account.
  2. Install Xcode: Visit the Apple App Store and install Xcode.
  3. Launch Xcode: Open Xcode by going to File > Export > iOS.

A Comprehensive Guide to Efficiently Writing and Implementing iOS Unit Tests

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