The ultimate guide to iOS Unit Testing with Swift and Xcode

Gurjit Singh
The Startup
Published in
2 min readJun 29, 2020

Photo by Marvin Meyer on Unsplash

Unit testing is a testing method where you can test “unit” of code whether it is working as you want or not. In Xcode, use XCTest framework to perform unit tests.

Unit test is a function starts with lowercase word "test” and it must be method of subclass of XCTestCase . It has conditions to check code is doing right as expected, but it has no parameters and no return value.

How to setup unit testing

Because units tests are perform under unit testing target you must have to add them before use. You can include “Unit Testing Bundle” in Xcode project two ways :

  • First, is to check “Include Unit Tests” while creating new project.
  • Another, way is to go to File > New > Target and search for “Include Unit Tests” .

After setup it will generate new subclass of XCTestCase in your project inside testing folder which you can find inside Project navigator.

import XCTest

class XCArticleTests: XCTestCase {

override func setUp() {
// method is called before each test method
// setup code here
override func tearDown() {
// method is called after each test method in the
// code to perform cleanup
func testExample() {
// add test case.
// Use XCTAssert to test code

This example defines XCArticleTests which is a subclass of XCTestCase . It has three methods setUp() for initial setup, tearDown() to perform cleanup after execution and test method called testExample to perform all tests. If you want to read more about setup and teardown methods go to link .

How to write unit tests

Define new extension of type Int with a function called cubed which returns cube number.

extension Int {
func cubed() -> Int {
return self * self * self

Define new XCTestCase subclass CubeNumberTests with a method named testCubeNumber(). This method creates two properties one is number and another for cubeNumber and checks cubeNumber equals to 125.

class CubeNumberTests: XCTestCase {

func testCubeNumber() {
let number = 5
let cubeNumber = number.cubed()
XCTAssertEqual(cubeNumber, 125)

Click on gray diamond button on the left side next to test method. The diamond turns into green if test passes or otherwise it will give error message. The above test will be succeed because cube number of 5 matches 125.


Unit testing is a necessary skill if you want to be a good developer. It look hard in the beginning but it gets easier as you use them. Don’t use unit tests all over your application it will be confusing and time wasting .You should use them when it’s too necessary.

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Gurjit Singh
The Startup

I’m Computer Science graduate and an iOS Engineer who writes about Swift and iOS development. Follow me on twitter @gurjitpt and for more articles