8.
Testing
Written by Saeed Taheri
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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.
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.
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.
As an example, choose android to run the test on Android.
Congratulations! You ran your first test successfully.
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.
private lateinit var viewModel: RemindersViewModel
@BeforeTest
fun setup() {
viewModel = RemindersViewModel()
}
@Test
fun testCreatingReminder() {
//1
val title = "New Title"
//2
viewModel.createReminder(title)
//3
val count = viewModel.reminders.count {
it.title == title
}
//4
assertTrue(
actual = count == 1,
message = "Reminder with title: $title wasn't created.",
)
}
internal val reminders: List<Reminder>
get() = repository.reminders
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.
expect class PlatformTest {
@Test
fun testOperatingSystemName()
}
Android
Create PlatformTest.kt inside the directories you created earlier in androidUnitTest and update as follows:
import kotlin.test.DefaultAsserter.assertEquals
actual class PlatformTest {
private val platform = Platform()
@Test
actual fun testOperatingSystemName() {
assertEquals(
expected = "Android",
actual = platform.osName,
message = "The OS name should be Android."
)
}
}
actual val cpuType =
Build.SUPPORTED_ABIS?.firstOrNull() ?: "---"
actual val screen: ScreenInfo
get() = ScreenInfo()
iOS
Create PlatformTest.kt inside the directories you created earlier in iosTest and update as follows:
import kotlin.test.Test
import kotlin.test.assertTrue
actual class PlatformTest {
private val platform = Platform()
@Test
actual fun testOperatingSystemName() {
assertTrue(
actual = platform.osName.equals("iOS", ignoreCase = true)
|| platform.osName == "iPadOS",
message = "The OS name should either be iOS or iPadOS."
)
}
}
Desktop
Create PlatformTest.kt inside the directories you created earlier in desktopMain and update as follows:
import kotlin.test.Test
import kotlin.test.assertTrue
actual class PlatformTest {
private val platform = Platform()
@Test
actual fun testOperatingSystemName() {
assertTrue(
actual = platform.osName.contains("Mac", ignoreCase = true)
|| platform.osName.contains("Windows", ignoreCase = true)
|| platform.osName.contains("Linux", ignoreCase = true)
|| platform.osName == "Desktop",
message = "Non-supported operating system"
)
}
}
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.
debugImplementation(libs.androidx.ui.test.manifest)
androidTestImplementation(platform(libs.androidx.compose.bom))
androidTestImplementation(libs.junit)
androidTestImplementation(libs.androidx.ui.test.junit4)
androidTestImplementation(libs.androidx.test.runner)
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
import androidx.compose.ui.test.junit4.createAndroidComposeRule
import com.yourcompany.organize.android.ui.root.MainActivity
import org.junit.Rule
class AppUITest {
@get:Rule
val composeTestRule = createAndroidComposeRule<MainActivity>()
}
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.
IconButton(
onClick = onAboutButtonClick,
modifier = Modifier.semantics { contentDescription = "aboutButton" },
) {
Icon(
imageVector = Icons.Outlined.Info,
contentDescription = "About Device Button",
)
}
@Test
fun testAboutButtonExistence() {
composeTestRule
.onNodeWithContentDescription("aboutButton")
.assertIsDisplayed()
}
@Test
fun testOpeningAndClosingAboutPage() {
//1
composeTestRule
.onNodeWithContentDescription("aboutButton")
.performClick()
//2
composeTestRule
.onNodeWithText("About Device")
.assertIsDisplayed()
//3
composeTestRule
.onNodeWithContentDescription("Up Button")
.performClick()
//4
composeTestRule
.onNodeWithText("Reminders")
.assertIsDisplayed()
}
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:
val desktopTest by getting {
dependencies {
implementation(compose.desktop.uiTestJUnit4)
implementation(compose.desktop.currentOs)
}
}
@Before
fun setUp() {
composeTestRule.setContent {
var screenState by remember { mutableStateOf(Screen.Reminders) }
when (screenState) {
Screen.Reminders ->
RemindersView(
onAboutButtonClick = { screenState = Screen.AboutDevice }
)
Screen.AboutDevice -> AboutView()
}
}
}
@Test
fun testOpeningAboutPage() {
//1
composeTestRule
.onNodeWithText("Reminders")
.assertIsDisplayed()
//2
composeTestRule
.onNodeWithContentDescription("aboutButton")
.performClick()
//3
composeTestRule.waitForIdle()
//4
composeTestRule
.onNodeWithContentDescription("aboutView")
.assertIsDisplayed()
}
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.
private let app = XCUIApplication()
override func setUp() {
continueAfterFailure = false
app.launch()
}
func testAboutButtonExistence() {
XCTAssert(app.buttons["About"].exists)
}
.accessibilityIdentifier("aboutButton")
Button {
shouldOpenAbout = true
} label: {
Label("About", systemImage: "info.circle")
.labelStyle(.titleAndIcon)
}
.accessibilityIdentifier("aboutButton")
.popover(isPresented: $shouldOpenAbout) {
AboutView()
.frame(
idealWidth: 350,
idealHeight: 450
)
}
XCTAssert(app.buttons["aboutButton"].exists)
Recording UI tests
Xcode has a cool feature that you can take advantage of to make the process of creating UI tests easier.
func testOpeningAndClosingAboutPage() {
// Put the cursor here
}
func testOpeningAndClosingAboutPage() {
let app = XCUIApplication()
app.navigationBars["Reminders"].buttons["aboutButton"].tap()
app.navigationBars["About Device"].buttons["Done"].tap()
}
func testOpeningAndClosingAboutPage() {
//1
app.buttons["aboutButton"].tap()
//2
let aboutPageTitle = app.staticTexts["About Device"]
XCTAssertTrue(aboutPageTitle.exists)
//3
app.navigationBars["About Device"].buttons["Done"].tap()
//4
let remindersPageTitle = app.staticTexts["Reminders"]
XCTAssertTrue(remindersPageTitle.exists)
}
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: