Chapters
Chapters

Chapters

Hide chapters

Kotlin Multiplatform by Tutorials

Third Edition · Android 15, iOS 18, Desktop · Kotlin 2.1.20 · Android Studio Meerkat

Before You Begin

Section 0: 5 chapters
Show chapters Hide chapters

Section I: Beginning Kotlin Multiplatform

Section 1: 5 chapters
Show chapters Hide chapters

Section II: Kotlin Multiplatform: Intermediate

Section 2: 5 chapters
Show chapters Hide chapters

Section III: Kotlin Multiplatform: Advanced

Section 3: 5 chapters
Show chapters Hide chapters

Section IV: Appendices

Section 4: 3 chapters
Show chapters Hide chapters

8. Testing
Written by Saeed Taheri

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Here it comes — that phase in software development that makes you want to procrastinate, no matter how important you know it really is.

Whether you like it or not, having a good set of tests — both automated and manual — ensures the quality of your software. When using Kotlin Multiplatform, you have enough tools at your hand to write tests. So if you’re thinking of letting it slide this time, you’ll have to come up with another excuse. :]

Setting Up the Dependencies

Testing your code in the KMP world follows the same pattern you’re now familiar with. You test the code in the common module. You may also need to use the expect/actual mechanism as well. With this in mind, setting up the dependencies is structurally the same as it is with non-test code.

From the starter project, using Android Studio, open the build.gradle.kts file inside the shared module. In the sourceSets block, there’s a block for commonTest source set after val commonMain by getting:

val commonTest by getting {
  dependencies {
    implementation(kotlin("test"))
  }
}

This is a dependency on the kotlin.test library. This library provides annotations to mark test functions and a set of utility functions needed for assertions in tests. Additionally, this line automatically includes all the platform dependencies.

Do a Gradle sync if required.

As you declared above, your test codes will be inside the commonTest folder. Create it as a sibling directory to commonMain by right-clicking the src folder inside the shared module and choosing New ▸ Directory. Once you start typing commonTest, Android Studio will provide you with autocompletion. Choose commonTest/kotlin.

Fig. 8.1 — Create a new directory in Android Studio
Fig. 8.1 — Create a new directory in Android Studio

Fig. 8.2 — Android Studio suggests naming the test directory
Fig. 8.2 — Android Studio suggests naming the test directory

Note: Although not necessary, it’s a good practice to have your test files in the same package structure as your main code. If you want to do that, type commonTest/kotlin/com/yourcompany/organize/presentation in the previous step, or create the nested directories manually afterward.

Next, create a class named RemindersViewModelTest inside the directory you just created. As the name implies, this class will have all the tests related to RemindersViewModel.

Now it’s time to create the very first test function for the app. Add this inside the newly created class:

@Test
fun testCreatingReminder() {
}

You’ll implement the function body later. The point to notice is the @Test annotation. It comes from the kotlin.test library. Make sure to import the needed package at the top of the file if Android Studio didn’t do it automatically for you: import kotlin.test.Test.

As soon as you add a function with @Test annotation to the class, Android Studio shows run buttons in the code gutter to make it easier for you to run the tests.

Fig. 8.3 — Run button for tests in code gutter
Fig. 8.3 — Run button for tests in code gutter

You can run the tests by clicking on those buttons, using commands in the terminal, or by pressing the keyboard shortcut Control-Shift-R on Mac or Control-Shift-F10 on Windows and Linux.

Fig. 8.4 — Choosing test platform
Fig. 8.4 — Choosing test platform

As an example, choose android to run the test on Android.

Congratulations! You ran your first test successfully.

Fig. 8.5 — First test successful
Fig. 8.5 — First test successful

When you ask the system to run the test on any platform, it needs to find a test library on that platform to run your tests on. By adding the dependency to kotlin-test in the commonSet source set, the Gradle plugin can infer the corresponding test dependencies for each test source set. For instance, it uses kotlin-test-junit for JVM-based source sets such as Android or Desktop. Kotlin Native source sets don’t require any additional test dependencies, as the implementations are built-in.

Writing Tests for RemindersViewModel

With the dependencies for unit testing all in place, it’s time to create some useful test functions.

Fef. 8.6 — Lloajusb ehxZenxr txot Qfujti tuto
Mun. 2.1 — Hzeumopx uxnSewwn nkuy Pbigli lequ

Foy. 4.8 — Hayliwtwaf tods vov gciijovh a cuxigpay
Yuz. 6.5 — Ledvunrqev zudt xij ymaifuzd o vovefvum

Writing Tests for Platform

All implementation details of the RemindersViewModel class were inside the commonMain source set. However, the Platform class is a bit different. As you remember, Platform uses the expect/actual mechanism. That means the implementation is different on each platform, and it produces different results.

Android

Create PlatformTest.kt inside the directories you created earlier in androidUnitTest and update as follows:

iOS

Create PlatformTest.kt inside the directories you created earlier in iosTest and update as follows:

Desktop

Create PlatformTest.kt inside the directories you created earlier in desktopMain and update as follows:

UI Tests

Until now, the approach you’ve followed in this book is to share the business logic in the shared module using Kotlin Multiplatform and create the UI in each platform using the available native toolkit. Consequently, you’ve been able to share the tests for the business logic inside the shared module as well.

Android

You created the UI for Organize entirely using Jetpack Compose. Testing Compose layouts is different from testing a View-based UI. The View-based UI toolkit defines what properties a View has, such as the rectangle it’s occupying, its properties and so forth. In Compose, some composables may emit UI into the hierarchy. Hence, you need a new matching mechanism for UI elements.

Semantics

Semantics give meaning to a piece of UI — whether it’s a simple button or a whole set of composables. The semantics framework is primarily there for accessibility purposes. However, tests can take advantage of the information exposed by semantics about the UI hierarchy.

Qaq. 5.8 — Fuzqikgtum mibr kas inoel molfer asuskexdi
Xig. 1.5 — Vintumlzim kept nus unauw vowbab ayeyvuxqe

Desktop

As the UI code for Android and desktop are essentially the same, the tests will be very similar. The setup is a bit different, though. The code is already there for you in the starter project. These are the differences you should consider:

iOS

To make the UI code testable in Xcode, you need to add a UI Test target to your project. While the iOS app project is open in Xcode, choose File ▸ New ▸ Target… from the menu bar.

Kum. 4.0 — Xdexu Zil Viwyog Xuvmlijo
Fex. 8.5 — Fnapa Sat Riccop Miprpifi

Pon. 8.68 — Kxebo OI Munb Jublov pacih
Qij. 2.93 — Skevu OI Gocy Kejgav zejuc

Recording UI tests

Xcode has a cool feature that you can take advantage of to make the process of creating UI tests easier.

Luf. 5.56 — Wwana EA Dofq Runegv xikfon
Qeh. 8.90 — Ybeke UE Sewn Dawajp besvag

Sem. 4.21 — Gzaxe EE Vedm Heccaml
Riw. 1.84 — Npaso AI Vucb Logkavn

Challenge

Here is a challenge for you to see if you’ve got the idea. The solution is inside the materials for this chapter.

Challenge: Writing Tests for RemindersRepository

Going one level deeper into the app’s architectural monument, it’s essential to have a bulletproof repository. After all, repositories are the backbone of the viewModels in Organize. Although it may seem effortless and similar to the viewModels at this time, you’ll see how these tests will play a vital role when you connect a database to the repository as you move forward.

Key Points

  • KMP will help you write less test code in the same way that it helped you write less business logic code.
  • You can write tests for your common code as well as for platform-specific code — all in Kotlin.
  • Declaring dependencies to a testing library for each platform is necessary. KMP will run your tests via the provided environment — such as JUnit on JVM.
  • Using expect/actual mechanisms in test codes is possible.
  • For UI tests, you consult each platform’s provided solution: Compose Tests for UIs created with Jetpack Compose and XCUITest for UIs created with UIKit or SwiftUI.

Where to Go From Here?

This chapter barely scratched the surface of testing. It didn’t discuss mocks and stubs, and it tried not to use third-party libraries, for that matter. There are a few libraries worth mentioning, though:

7. App Architecture
9. Dependency Injection
Have a technical question? Want to report a bug? You can ask questions and report bugs to the book authors in our official book forum here.
© 2026 Kodeco Inc.

You’re accessing parts of this content for free, with some sections shown as scrambled text. Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now