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[Video](https://www.youtube.com/watch?v=Y9GWnwi9D0I)
You can test your Compose app with well-established approaches and patterns.
### Test in isolation
[`ComposeTestRule`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/junit4/ComposeTestRule) lets you start an activity displaying any composable:
your full application, a single screen, or a small element. It's also a good
practice to check that your composables are correctly encapsulated and they work
independently, allowing for easier and more focused UI testing.
This doesn't mean you should *only* create unit UI tests. UI tests scoping
larger parts of your UI are also very important.
### Access the activity and resources after setting your own content
Oftentimes you need to set the content under test using
`composeTestRule.setContent` and you also need to access activity resources, for
example to assert that a displayed text matches a string resource. However, you
can't call `setContent` on a rule created with `createAndroidComposeRule()` if
the activity already calls it.
A common pattern to achieve this is to create an `AndroidComposeTestRule` using
an empty activity such as [`ComponentActivity`](https://developer.android.com/reference/androidx/activity/ComponentActivity).
class MyComposeTest {
@get:Rule
val composeTestRule = createAndroidComposeRule<ComponentActivity>()
@Test
fun myTest() {
// Start the app
composeTestRule.setContent {
MyAppTheme {
MainScreen(uiState = exampleUiState, /*...*/)
}
}
val continueLabel = composeTestRule.activity.getString(R.string.next)
composeTestRule.onNodeWithText(continueLabel).performClick()
}
}
Note that `ComponentActivity` needs to be added to your app's
`AndroidManifest.xml` file. Enable that by adding this dependency to your
module:
debugImplementation("androidx.compose.ui:ui-test-manifest:$compose_version")
### Custom semantics properties
You can create custom [semantics](https://developer.android.com/develop/ui/compose/testing/semantics) properties to expose information to tests.
To do this, define a new `SemanticsPropertyKey` and make it available using the
`SemanticsPropertyReceiver`.
// Creates a semantics property of type Long.
val PickedDateKey = SemanticsPropertyKey<Long>("PickedDate")
var SemanticsPropertyReceiver.pickedDate by PickedDateKey
Now use that property in the `semantics` modifier:
val datePickerValue by remember { mutableStateOf(0L) }
MyCustomDatePicker(
modifier = Modifier.semantics { pickedDate = datePickerValue }
)
From tests, use `SemanticsMatcher.expectValue` to assert the value of the
property:
composeTestRule
.onNode(SemanticsMatcher.expectValue(PickedDateKey, 1445378400)) // 2015-10-21
.assertExists()
> [!WARNING]
> **Warning:** You should only use custom Semantics properties when it's hard to match a specific item using the given finders and matchers. Using custom Semantics properties to expose visual properties such as colors, font size or rounded corner radius is not recommended, as it can pollute production code and wrong implementations can lead to bugs that are hard to find.
### Verify state restoration
Verify that the state of your Compose elements is correctly restored when the
activity or process is recreated. Perform such checks without relying on
activity recreation with the [`StateRestorationTester`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/junit4/StateRestorationTester) class.
This class lets you simulate the recreation of a composable. It's especially
useful to verify the implementation of [`rememberSaveable`](https://developer.android.com/reference/kotlin/androidx/compose/runtime/saveable/rememberSaveable.composable#rememberSaveable(kotlin.Array,androidx.compose.runtime.saveable.Saver,kotlin.String,kotlin.Function0)).
class MyStateRestorationTests {
@get:Rule
val composeTestRule = createComposeRule()
@Test
fun onRecreation_stateIsRestored() {
val restorationTester = StateRestorationTester(composeTestRule)
restorationTester.setContent { MainScreen() }
// TODO: Run actions that modify the state
// Trigger a recreation
restorationTester.emulateSavedInstanceStateRestore()
// TODO: Verify that state has been correctly restored.
}
}
### Test different device configurations
Android apps need to adapt to many changing conditions: window sizes, locales,
font sizes, dark and light themes, and more. Most of these conditions are
derived from device-level values controlled by the user and exposed with the
current [`Configuration`](https://developer.android.com/reference/android/content/res/Configuration) instance. Testing different configurations
directly in a test is difficult since the test must configure device-level
properties.
[`DeviceConfigurationOverride`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride) is a test-only API that lets you simulate
different device configurations in a localized way for the `@Composable` content
under test.
The companion object of `DeviceConfigurationOverride` has the following
extension functions, which override device-level configuration properties:
- [`DeviceConfigurationOverride.DarkMode()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.Companion#(androidx.compose.ui.test.DeviceConfigurationOverride.Companion).DarkMode(kotlin.Boolean)): Overrides the system to dark theme or light theme.
- [`DeviceConfigurationOverride.FontScale()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.Companion#(androidx.compose.ui.test.DeviceConfigurationOverride.Companion).FontScale(kotlin.Float)): Overrides the [system font
scale](https://developer.android.com/training/multiscreen/screendensities#TaskUseDP).
- [`DeviceConfigurationOverride.FontWeightAdjustment()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.Companion#(androidx.compose.ui.test.DeviceConfigurationOverride.Companion).FontWeightAdjustment(kotlin.Int)): Overrides the system font weight adjustment.
- [`DeviceConfigurationOverride.ForcedSize()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.Companion#(androidx.compose.ui.test.DeviceConfigurationOverride.Companion).ForcedSize(androidx.compose.ui.unit.DpSize)): Forces a specific amount of space regardless of device size.
- [`DeviceConfigurationOverride.LayoutDirection()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.Companion#(androidx.compose.ui.test.DeviceConfigurationOverride.Companion).LayoutDirection(androidx.compose.ui.unit.LayoutDirection)): Overrides the [layout
direction](https://developer.android.com/training/basics/supporting-devices/languages#SupportLayoutMirroring) (left-to-right or right-to-left).
- [`DeviceConfigurationOverride.Locales()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.Companion#(androidx.compose.ui.test.DeviceConfigurationOverride.Companion).Locales(androidx.compose.ui.text.intl.LocaleList)): Overrides the [locale](https://developer.android.com/guide/topics/resources/localization).
- [`DeviceConfigurationOverride.RoundScreen()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.Companion#(androidx.compose.ui.test.DeviceConfigurationOverride.Companion).RoundScreen(kotlin.Boolean)): Overrides if the screen is [round](https://developer.android.com/design/ui/wear/guides/foundations/getting-started#design-for-round).
To apply a specific override, wrap the content under test in a call to the
[`DeviceConfigurationOverride()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride.composable#DeviceConfigurationOverride(androidx.compose.ui.test.DeviceConfigurationOverride,kotlin.Function0)) top-level function, passing the override
to apply as a parameter.
For example, the following code applies the
`DeviceConfigurationOverride.ForcedSize()` override to change the density
locally, forcing the `MyScreen` composable to be rendered in a large landscape
window, even if the device the test is running on doesn't support that window
size directly:
```kotlin
composeTestRule.setContent {
DeviceConfigurationOverride(
DeviceConfigurationOverride.ForcedSize(DpSize(1280.dp, 800.dp))
) {
MyScreen() // Will be rendered in the space for 1280dp by 800dp without clipping.
}
}
```
<br />
To apply multiple overrides together, use
[`DeviceConfigurationOverride.then()`](https://developer.android.com/reference/kotlin/androidx/compose/ui/test/DeviceConfigurationOverride#(androidx.compose.ui.test.DeviceConfigurationOverride).then(androidx.compose.ui.test.DeviceConfigurationOverride)):
```kotlin
composeTestRule.setContent {
DeviceConfigurationOverride(
DeviceConfigurationOverride.FontScale(1.5f) then
DeviceConfigurationOverride.FontWeightAdjustment(200)
) {
Text(text = "text with increased scale and weight")
}
}
```
<br />
## Additional Resources
- **[Test apps on Android](https://developer.android.com/training/testing)**: The main Android testing landing page provides a broader view of testing fundamentals and techniques.
- **[Fundamentals of testing](https://developer.android.com/training/testing/fundamentals):** Learn more about the core concepts behind testing an Android app.
- **[Local tests](https://developer.android.com/training/testing/local-tests):** You can run some tests locally, on your own workstation.
- **[Instrumented tests](https://developer.android.com/training/testing/instrumented-tests):** It is good practice to also run instrumented tests. That is, tests that run directly on-device.
- **[Continuous integration](https://developer.android.com/training/testing/continuous-integration):** Continuous integration lets you integrate your tests into your deployment pipeline.
- **[Test different screen sizes](https://developer.android.com/training/testing/different-screens):** With some many devices available to users, you should test for different screen sizes.
- **[Espresso](https://developer.android.com/training/testing/espresso)**: While intended for View-based UIs, Espresso knowledge can still be helpful for some aspects of Compose testing.

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> [!WARNING]
> **Experimental:** Compose Preview Screenshot Testing is still in development. Its features and APIs are subject to change substantially during the alpha phase. Report any feedback and issues through the [issue tracker](https://issuetracker.google.com/issues/new?component=192708&template=840533).
Screenshot testing is an effective way to verify how your UI looks to users.
The Compose Preview Screenshot Testing tool combines the simplicity and
features of [composable previews](https://developer.android.com/develop/ui/compose/tooling/previews) with the productivity
gains of running host-side screenshot tests. Compose Preview Screenshot Testing
is designed to be as straightforward to use as composable previews.
A screenshot test is an automated test that takes a screenshot of a piece of UI
and then compares it against a previously approved reference image. If the
images don't match, the test fails and produces an HTML report to help you
compare and find the differences.
With the Compose Preview Screenshot Testing tool, you can:
- Use `@PreviewTest` to create screenshot tests for existing or new composable previews.
- Generate reference images from those composable previews.
- Generate an HTML report that identifies changes to those previews after you make code changes.
- Use `@Preview` parameters, such as `uiMode` or `fontScale`, and multi-previews to help you scale your tests.
- Modularize your tests with the new `screenshotTest` source set.
![](https://developer.android.com/static/studio/images/compose-screenshot-testing.png) **Figure 1.** Example HTML report.
## IDE integration
While you can use the Compose Preview Screenshot Testing tool by running the
underlying Gradle tasks (`updateScreenshotTest` and `validateScreenshotTest`)
manually, Android Studio Otter 3 Feature Drop Canary 4 introduces a full IDE
integration. This lets you generate reference images, run tests, and analyze
validation failures entirely within the IDE. Here are some of the key features:
- **In-editor gutter icons.** You can now run tests or update reference images directly from the source code. Green run icons appear in the gutter next to composables and classes annotated with `@PreviewTest`.
- **Run screenshot tests.** Execute tests specifically for a single function or for an entire class.
- **Add or update reference images.** Trigger the update flow specifically for the selected scope.
- **Interactive reference management.** Updating reference images is now safer and more granular.
- **New reference image generation dialog.** Instead of running a bulk Gradle task, a new dialog lets you visualize and select exactly which previews to generate or update.
- **Preview variations.** The dialog lists all preview variations (such as light theme or dark theme, or different devices) individually, allowing you to select or clear specific items before generating images.
- **Integrated test results and diff viewer.** View results without leaving the IDE.
- **Unified run panel.** Screenshot test results appear in the standard **Run** tool window. Tests are grouped by class and function, with pass or fail status clearly marked.
- **Visual diff tool.** When a test fails, the **Screenshot** tab lets you compare the *Reference* , *Actual* , and *Diff* images side-by-side.
- **Detailed attributes.** An **Attributes** tab provides metadata on failed tests, including match percentage, image dimensions, and the specific preview configuration used (for example, `uiMode` or `fontScale`).
- **Flexible test scoping.** You can now execute screenshot tests with various scopes directly from the Project View. Right-click a module, directory, file, or class to run screenshot tests specifically for that selection.
## Requirements
To use Compose Preview Screenshot Testing through the full IDE integration, your
project must meet the following requirements:
- Android Studio Panda 1 Canary 4 or higher.
- Android Gradle Plugin (AGP) version 9.0 or higher.
- Compose Preview Screenshot Testing plugin version [0.0.1-alpha15](https://developer.android.com/studio/preview/compose-screenshot-testing-release-notes#alpha15) or higher.
- Kotlin version 2.2.10 or higher.
- JDK version 17 or higher.
- Compose enabled for your project. We recommend enabling Compose using the [Compose Compiler Gradle plugin](https://developer.android.com/develop/ui/compose/compiler).
If you only want to use the underlying Gradle tasks without the IDE integration,
the requirements are as follows:
- Android Gradle Plugin (AGP) version 8.5.0 or higher.
- Compose Preview Screenshot Testing plugin version [0.0.1-alpha15](https://developer.android.com/studio/preview/compose-screenshot-testing-release-notes#alpha15) or higher.
- Kotlin version 1.9.20 or higher. We recommend using Kotlin 2.0 or higher so you can use the Compose Compiler Gradle plugin.
- JDK version 17 or higher.
- Compose enabled for your project. We recommend enabling Compose using the [Compose Compiler Gradle plugin](https://developer.android.com/develop/ui/compose/compiler).
> [!NOTE]
> **Note:** If you can't use the Compose Compiler Gradle plugin, you can enable Compose by [declaring a dependency on the Compose Compiler directly](https://developer.android.com/jetpack/androidx/releases/compose-kotlin#kts). Make sure you use `kotlinCompilerExtensionVersion` version 1.5.4 or higher.
## Setup
Both the integrated tool and the underlying Gradle tasks rely on the Compose
Preview Screenshot Testing plugin. To set up the plugin, follow these steps:
1. Enable the experimental property in your project's `gradle.properties` file.
android.experimental.enableScreenshotTest=true
2. In the `android {}` block of your module-level `build.gradle.kts` file,
enable the experimental flag to use the `screenshotTest` source set.
android {
experimentalProperties["android.experimental.enableScreenshotTest"] = true
}
3. Add the `com.android.compose.screenshot` plugin, version `0.0.1-alpha15` to
your project.
1. Add the plugin to your version catalogs file:
[versions]
agp = "9.0.0-rc03"
kotlin = "2.2.10"
screenshot = "0.0.1-alpha15"
[plugins]
screenshot = { id = "com.android.compose.screenshot", version.ref = "screenshot"}
2. In your module-level `build.gradle.kts` file, add the plugin in the
`plugins {}` block:
plugins {
alias(libs.plugins.screenshot)
}
4. Add the [`screenshot-validation-api`](https://maven.google.com/web/index.html?q=screenshot-validation-api#com.android.tools.screenshot:screenshot-validation-api)
and [`ui-tooling`](https://maven.google.com/web/index.html?q=tooling#androidx.compose.ui:ui-tooling)
dependencies.
1. Add them to your version catalogs:
[libraries]
screenshot-validation-api = { group = "com.android.tools.screenshot", name = "screenshot-validation-api", version.ref = "screenshot"}
androidx-ui-tooling = { group = "androidx.compose.ui", name = "ui-tooling"}
2. Add them to your module-level `build.gradle.kts` file:
dependencies {
screenshotTestImplementation(libs.screenshot.validation.api)
screenshotTestImplementation(libs.androidx.ui.tooling)
}
## Designate composable previews to use for screenshot tests
To designate the composable previews you want to use for screenshot tests, mark
the previews with the `@PreviewTest` annotation. The previews must be located in
the new `screenshotTest` source set, for example:
`app/src/screenshotTest/kotlin/com/example/yourapp/`
`ExamplePreviewScreenshotTest.kt`
You can add more composables or previews, including multi-previews, in
this file or other files created in the same source set.
package com.example.yourapp
import androidx.compose.runtime.Composable
import androidx.compose.ui.tooling.preview.Preview
import com.android.tools.screenshot.PreviewTest
import com.example.yourapp.ui.theme.MyApplicationTheme
@PreviewTest
@Preview(showBackground = true)
@Composable
fun GreetingPreview() {
MyApplicationTheme {
Greeting("Android!")
}
}
## Generate reference images
After you set up a test class, you need to generate reference images for each
preview. These reference images are used to identify changes later, after you
make code changes. To generate reference images for your composable preview
screenshot tests, follow the instructions in this section for the IDE
integration or for the Gradle tasks.
### In the IDE
Click the gutter icon next to a `@PreviewTest` function and select **Add/Update
Reference Images** . Select the previews in the dialog and click **Add**.
### With the Gradle tasks
Run the following Gradle task:
- Linux and macOS: `./gradlew updateDebugScreenshotTest` (`./gradlew :{module}:update{Variant}ScreenshotTest`)
- Windows: `gradlew updateDebugScreenshotTest` (`gradlew :{module}:update{Variant}ScreenshotTest`)
After the task completes, find the reference images in
`app/src/screenshotTestDebug/reference`
(`{module}/src/screenshotTest{Variant}/reference`).
> [!NOTE]
> **Note:** The reference images are named with a concatenation of the fully-qualified name of the test function and a hash of the preview parameters, for example `com.sample.screenshottests.test1_da39a3ee_c2200e98_0.png`.
## Generate a test report
Once the reference images exist, generate a test report by following the
instructions in this section for the IDE integration or for the Gradle tasks.
### In the IDE
Click the gutter icon next to a `@PreviewTest` function and select **Run
'ScreenshotTests'**.
If a test fails, click the test name in the **Run** panel. Select the
**Screenshot** tab to inspect the image diff using the integrated zoom and pan
controls.
> [!NOTE]
> **Note:** Renaming a function annotated with `@PreviewTest` breaks the association with existing reference images. In that case, you must [regenerate reference images](https://developer.android.com/studio/preview/compose-screenshot-testing#generate-reference-images) for the new function name.
### With the Gradle tasks
Run the validate task to take a new screenshot and compare it with the
reference image:
- Linux and macOS: `./gradlew validateDebugScreenshotTest` (`./gradlew :{module}:validate{Variant}ScreenshotTest`)
- Windows: `gradlew validateDebugScreenshotTest` (`gradlew :{module}:validate{Variant}ScreenshotTest`)
The verification task creates an HTML report at
`{module}/build/reports/screenshotTest/preview/{variant}/index.html`.
## Troubleshooting
Compose Preview Screenshot Testing runs host-side tests, which can be
memory-intensive. You can increase the maximum heap size for the test JVM by
adding the following property to your `gradle.properties` file:
android.compose.screenshot.maxHeapSize=4g
## Known issues
- **Kotlin Multiplatform (KMP):** Both the IDE and the underlying plugin are engineered exclusively for Android projects. They don't support non-Android targets in KMP projects.
You can find the complete list of current known issues in the tool's
[issue tracker component](https://issuetracker.google.com/issues?q=status:open+componentid:1581441&s=created_time:desc). Report any other feedback and issues
through the [issue tracker](https://issuetracker.google.com/issues/new?component=192708&template=840533).
## Release updates
For a full list of release updates, see the
[release notes](https://developer.android.com/studio/preview/compose-screenshot-testing-release-notes).

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One of the benefits of using dependency injection frameworks like Hilt is that
it makes testing your code easier.
## Unit tests
Hilt isn't necessary for unit tests, since when testing a class that uses
constructor injection, you don't need to use Hilt to instantiate that class.
Instead, you can directly call a class constructor by passing in fake or mock
dependencies, just as you would if the constructor weren't annotated:
```kotlin
@ActivityScoped
class AnalyticsAdapter @Inject constructor(
private val service: AnalyticsService
) { ... }
class AnalyticsAdapterTest {
@Test
fun `Happy path`() {
// You don't need Hilt to create an instance of AnalyticsAdapter.
// You can pass a fake or mock AnalyticsService.
val adapter = AnalyticsAdapter(fakeAnalyticsService)
assertEquals(...)
}
}
```
The same applies to ViewModel classes obtained by calling `hiltViewModel()` in
your composables. In unit tests, construct the ViewModel directly with fakes.
For information on how state flows from a ViewModel into composables, see
[State and Jetpack Compose](https://developer.android.com/develop/ui/compose/state) and [Where to hoist state](https://developer.android.com/develop/ui/compose/state-hoisting).
## End-to-end tests
For integration tests, Hilt injects dependencies as it would in your production
code. Testing with Hilt requires no maintenance because Hilt automatically
generates a new set of components for each test.
### Adding testing dependencies
To use Hilt in your tests, include the `hilt-android-testing` dependency in your
project:
```kotlin
dependencies {
// For Robolectric tests.
testImplementation("com.google.dagger:hilt-android-testing:2.57.1")
kspTest("com.google.dagger:hilt-android-compiler:2.57.1")
// For instrumented tests.
androidTestImplementation("com.google.dagger:hilt-android-testing:2.57.1")
kspAndroidTest("com.google.dagger:hilt-android-compiler:2.57.1")
// Compose UI test rule.
androidTestImplementation("androidx.compose.ui:ui-test-junit4")
debugImplementation("androidx.compose.ui:ui-test-manifest")
}
```
> [!NOTE]
> **Note:** If you use [Jetpack integrations](https://developer.android.com/training/dependency-injection/hilt-jetpack) (like `hilt-navigation-compose` to obtain a ViewModel through `hiltViewModel()`), you must also add their annotation processors to your test dependencies.
### UI test setup
You must annotate any UI test that uses Hilt with `@HiltAndroidTest`. This
annotation is responsible for generating the Hilt components for each test.
Also, you need to add the `HiltAndroidRule` to the test class. It manages the
components' state and is used to perform injection on your test:
```kotlin
@HiltAndroidTest
class SettingsScreenTest {
@get:Rule(order = 0)
val hiltRule = HiltAndroidRule(this)
@get:Rule(order = 1)
val composeRule = createAndroidComposeRule<HiltTestActivity>()
// Compose UI tests here.
}
```
> [!NOTE]
> **Note:** If you have other rules in your test, see [Multiple TestRule objects in
> your instrumented test](https://developer.android.com/training/dependency-injection/hilt-testing#multiple-testrules).
Next, your test needs to know about the `Application` class that Hilt
automatically generates for you.
To let Hilt inject dependencies, you must create an empty activity named
`HiltTestActivity` in your `androidTest` source set and annotate it with
`@AndroidEntryPoint`. `createAndroidComposeRule` then uses this activity as the
host for your composable content.
#### Test application
You must execute instrumented tests that use Hilt in an `Application` object
that supports Hilt. The library provides `HiltTestApplication` for use in tests.
If your tests need a different base application, see [Custom application for
tests](https://developer.android.com/training/dependency-injection/hilt-testing#custom-application).
You must set your test application to run in your [instrumented
tests](https://developer.android.com/training/testing/ui-testing) or [Robolectric
tests](http://robolectric.org/). The following instructions aren't
specific to Hilt, but are general guidelines on how to specify a custom
application to run in tests.
##### Set the test application in instrumented tests
To use the Hilt test application in [instrumented
tests](https://developer.android.com/training/testing/ui-testing), you need to configure a new test runner.
This makes Hilt work for all of the instrumented tests in your project. Perform
the following steps:
1. Create a custom class that extends [`AndroidJUnitRunner`](https://developer.android.com/reference/kotlin/androidx/test/runner/AndroidJUnitRunner) in the `androidTest` folder.
2. Override the `newApplication` function and pass in the name of the generated Hilt test application.
```kotlin
// A custom runner to set up the instrumented application class for tests.
class CustomTestRunner : AndroidJUnitRunner() {
override fun newApplication(cl: ClassLoader?, name: String?, context: Context?): Application {
return super.newApplication(cl, HiltTestApplication::class.java.name, context)
}
}
```
Next, configure this test runner in your Gradle file as described in the
[instrumented unit test
guide](https://developer.android.com/training/testing/unit-testing/instrumented-unit-tests#setup). Make sure
you use the full classpath:
```kotlin
android {
defaultConfig {
// Replace com.example.android.dagger with your class path.
testInstrumentationRunner = "com.example.android.dagger.CustomTestRunner"
}
}
```
##### Set the test application in Robolectric tests
If you use Robolectric to test your UI layer, you can specify which application
to use in the `robolectric.properties` file:
`application = dagger.hilt.android.testing.HiltTestApplication`
Alternatively, you can configure the application on each test individually by
using Robolectric's `@Config` annotation:
```kotlin
@HiltAndroidTest
@Config(application = HiltTestApplication::class)
class SettingsScreenTest {
@get:Rule
var hiltRule = HiltAndroidRule(this)
// Robolectric tests here.
}
```
### Testing features
Once Hilt is ready to use in your tests, you can use several features to
customize the testing process.
#### Inject types in tests
To inject types into a test, use `@Inject` for field injection. To tell Hilt to
populate the `@Inject` fields, call `hiltRule.inject()`.
See the following example of an instrumented test:
```kotlin
@HiltAndroidTest
class SettingsScreenTest {
@get:Rule(order = 0)
val hiltRule = HiltAndroidRule(this)
@get:Rule(order = 1)
val composeRule = createAndroidComposeRule<HiltTestActivity>()
@Inject
lateinit var analyticsAdapter: AnalyticsAdapter
@Before
fun init() {
hiltRule.inject()
}
@Test
fun settingsScreen_showsTitle() {
composeRule.setContent {
SettingsScreen()
}
composeRule.onNodeWithText("Settings").assertIsDisplayed()
// analyticsRepository is available here.
}
}
```
#### Replace a binding
If you need to inject a fake or mock instance of a dependency, you need to tell
Hilt not to use the binding that it used in production code and to use a
different one instead. To replace a binding, you need to replace the module that
contains the binding with a test module that contains the bindings that you want
to use in the test.
For example, suppose your production code declares a binding for
`AnalyticsService` as follows:
```kotlin
@Module
@InstallIn(SingletonComponent::class)
abstract class AnalyticsModule {
@Singleton
@Binds
abstract fun bindAnalyticsService(
analyticsServiceImpl: AnalyticsServiceImpl
): AnalyticsService
}
```
To replace the `AnalyticsService` binding in tests, create a new Hilt module in
the `test` or `androidTest` folder with the fake dependency and annotate it
with `@TestInstallIn`. All the tests in that folder are injected with the fake
dependency instead.
```kotlin
@Module
@TestInstallIn(
components = [SingletonComponent::class],
replaces = [AnalyticsModule::class]
)
abstract class FakeAnalyticsModule {
@Singleton
@Binds
abstract fun bindAnalyticsService(
fakeAnalyticsService: FakeAnalyticsService
): AnalyticsService
}
```
Because composables typically consume these dependencies indirectly through a
ViewModel obtained with `hiltViewModel()`, replacing the binding in Hilt is
enough. The composable under test picks up the fake automatically.
#### Replace a binding in a single test
To replace a binding in a single test instead of all tests, uninstall a Hilt
module from a test using the `@UninstallModules` annotation and create a new
test module inside the test.
Following the `AnalyticsService` example from the previous version, begin by
telling Hilt to ignore the production module by using the `@UninstallModules`
annotation in the test class:
```kotlin
@UninstallModules(AnalyticsModule::class)
@HiltAndroidTest
class SettingsScreenTest { ... }
```
Next, you must replace the binding. Create a new module within the test class
that defines the test binding:
```kotlin
@UninstallModules(AnalyticsModule::class)
@HiltAndroidTest
class SettingsScreenTest {
@Module
@InstallIn(SingletonComponent::class)
abstract class TestModule {
@Singleton
@Binds
abstract fun bindAnalyticsService(
fakeAnalyticsService: FakeAnalyticsService
): AnalyticsService
}
// ...
}
```
This only replaces the binding for a single test class. If you want to replace
the binding for all test classes, use the `@TestInstallIn` annotation from the
section above. Alternatively, you can put the test binding in the `test` module
for Robolectric tests, or in the `androidTest` module for instrumented tests.
The recommendation is to use `@TestInstallIn` whenever possible.
> [!WARNING]
> **Warning:** You cannot uninstall modules that are not annotated with `@InstallIn`. Attempting to do so causes a compilation error.
> [!WARNING]
> **Warning:** `@UninstallModules` can only uninstall `@InstallIn` modules, not `@TestInstallIn` modules. Attempting to do so causes a compilation error.
> [!NOTE]
> **Note:** As Hilt creates new components for tests that use `@UninstallModules`, it can significantly impact unit test build times. Use it when necessary and prefer using `@TestInstallIn` when the bindings need to be replaced in all test classes.
#### Binding new values
Use the `@BindValue` annotation to easily bind fields in your test into the Hilt
dependency graph. Annotate a field with `@BindValue` and it will be bound under
the declared field type with any qualifiers that are present for that field.
In the `AnalyticsService` example, you can replace `AnalyticsService` with a
fake by using `@BindValue`:
```kotlin
@UninstallModules(AnalyticsModule::class)
@HiltAndroidTest
class SettingsScreenTest {
@BindValue @JvmField
val analyticsService: AnalyticsService = FakeAnalyticsService()
...
}
```
This simplifies both replacing a binding and referencing a binding in your test
by allowing you to do both at the same time.
`@BindValue` works with qualifiers and other testing annotations. For example,
if you use testing libraries such as
[Mockito](https://site.mockito.org/), you could use it in a
Robolectric test as follows:
```kotlin
...
class SettingsScreenTest {
...
@BindValue @ExampleQualifier @Mock
lateinit var qualifiedVariable: ExampleCustomType
// Robolectric tests here
}
```
If you need to add a [multibinding](https://dagger.dev/dev-guide/multibindings),
you can use the `@BindValueIntoSet` and `@BindValueIntoMap` annotations in place
of `@BindValue`. `@BindValueIntoMap` requires you to also annotate the field
with a map key annotation.
## Special cases
Hilt also provides features to support nonstandard use cases.
### Custom application for tests
If you cannot use `HiltTestApplication` because your test application needs to
extend another application, annotate a new class or interface with
`@CustomTestApplication`, passing in the value of the base class you want the
generated Hilt application to extend.
`@CustomTestApplication` will generate an `Application` class ready for testing
with Hilt that extends the application you passed as a parameter.
```kotlin
@CustomTestApplication(BaseApplication::class)
interface HiltTestApplication
```
In the example, Hilt generates an `Application` named
`HiltTestApplication_Application` that extends the `BaseApplication` class. In
general, the name of the generated application is the name of the annotated
class appended with `_Application`. You must set the generated Hilt test
application to run in your [instrumented tests](https://developer.android.com/training/testing/ui-testing) or
[Robolectric tests](http://robolectric.org/) as described in [Test
application](https://developer.android.com/training/dependency-injection/hilt-testing#test-application).
> [!NOTE]
> **Note:** Because `HiltTestApplication_Application` is code that Hilt generates at runtime, the IDE might highlight it in red until you run your tests.
### Multiple TestRule objects in your instrumented test
Compose UI tests already combine `HiltAndroidRule` with a Compose test rule
such as `createAndroidComposeRule`. If you have additional `TestRule` objects,
make sure `HiltAndroidRule` runs first. Declare the execution order with the
`order` attribute on `@Rule`:
```kotlin
@HiltAndroidTest
class SettingsScreenTest {
@get:Rule(order = 0)
var hiltRule = HiltAndroidRule(this)
@get:Rule(order = 1)
val composeRule = createAndroidComposeRule<HiltTestActivity>()
@get:Rule(order = 2)
val otherRule = SomeOtherRule()
// UI tests here.
}
```
Alternatively, you can wrap the rules with `RuleChain`, placing
`HiltAndroidRule` as the outer rule.
```kotlin
@HiltAndroidTest
class SettingsScreenTest {
@get:Rule
var rule = RuleChain.outerRule(HiltAndroidRule(this)).
around(SettingsScreenTestRule(...))
// UI tests here.
}
```
### Use an entry point before the singleton component is available
The `@EarlyEntryPoint` annotation provides an escape hatch when a Hilt entry
point needs to be created before the singleton component is available in a
Hilt test.
More information about `@EarlyEntryPoint` in the
[Hilt documentation](https://dagger.dev/hilt/early-entry-point).
## Additional resources
To learn more about testing, see the following additional resources:
### Documentation
- [Test your Compose layout](https://developer.android.com/develop/ui/compose/testing)
- [Testing cheatsheet](https://developer.android.com/develop/ui/compose/testing/testing-cheatsheet)
### Views content
- [Hilt testing guide (Views)](https://developer.android.com/topic/architecture/views/dependency-injection/hilt-testing-views)