Organizing Test Source Sets

commonTest
└── androidCommonTest          (helpers shared by host + device)
    ├── androidDeviceTest      (instrumentation APK on emulator/device)
    └── androidHostTest        (Robolectric on JVM)

// :feature:home/build.gradle.kts — production module
plugins { id("com.android.library") }

dependencies {
    testImplementation(project(":feature:home-testing"))
    androidTestImplementation(project(":feature:home-testing"))
}

// :feature:home-testing/build.gradle.kts — pure Kotlin or Android-library "test fixtures"
plugins { id("java-library") }   // or com.android.library if Android types needed

Where does this test go?
│
├── Pure Kotlin/JVM logic, no Android framework      → src/test/
│   (testImplementation deps)
│
├── Robolectric (Android framework simulated on JVM) → src/test/
│   (testImplementation deps + Robolectric)
│   NOT src/androidTest/.
│
├── ViewModel + coroutines + fakes                   → src/test/
│
├── Real Room database integration                    → src/androidTest/
│   (small instrumented test per /fundamentals)
│
├── Espresso UI test                                  → src/androidTest/
├── UiAutomator cross-app test                        → src/androidTest/
├── Compose UI test against real Activity            → src/androidTest/
│   + debugImplementation("...:ui-test-manifest")
│
├── Compose UI test on Robolectric                    → src/test/
│   (testImplementation("...:ui-test-junit4") + Robolectric)
│
├── Test helper (FakeRepository, MainDispatcherRule)  → :core-testing module OR src/sharedTest/
│   (with the AGP 7.2+ caveats above)

// WRONG — Espresso on testImplementation
dependencies {
    testImplementation("androidx.test.espresso:espresso-core:3.7.0")
    testImplementation("androidx.test.ext:junit:1.3.0")
}
// WRONG because: Espresso requires a real or simulated Android device. testImplementation
// only puts the JAR on the JVM classpath. The test compiles but ClassNotFoundException /
// IllegalStateException at runtime when Espresso looks for an Instrumentation instance.

// RIGHT — Espresso on androidTestImplementation
dependencies {
    androidTestImplementation("androidx.test.espresso:espresso-core:3.7.0")
    androidTestImplementation("androidx.test.ext:junit:1.3.0")
}

// WRONG
// src/androidTest/java/com/example/SomeRobolectricTest.kt
@RunWith(RobolectricTestRunner::class)
class SomeRobolectricTest { /* ... */ }
// WRONG because: Robolectric is a JVM Android simulator (per /fundamentals: "Big local test:
// You can use an Android simulator that runs locally, such as Robolectric"). It belongs in
// src/test/. Putting it in src/androidTest/ either fails to find Robolectric (which is on
// testImplementation) or runs it on the device JVM where its shadow mechanism does not work.

// RIGHT
// src/test/java/com/example/SomeRobolectricTest.kt
@RunWith(AndroidJUnit4::class)         // dispatches to Robolectric on JVM
@Config(sdk = [Build.VERSION_CODES.UPSIDE_DOWN_CAKE])
class SomeRobolectricTest { /* ... */ }

// WRONG
dependencies {
    androidTestImplementation("androidx.compose.ui:ui-test-junit4")
    androidTestImplementation("androidx.compose.ui:ui-test-manifest")  // wrong config
}
// WRONG because: ui-test-manifest contributes <activity android:name="ComponentActivity">
// to the merged debug APK manifest. On androidTestImplementation, the merger does not pick
// it up; createComposeRule() crashes with ActivityNotFoundException. Lint also flags this
// as TestManifestGradleConfiguration (WARNING).

// RIGHT
dependencies {
    androidTestImplementation("androidx.compose.ui:ui-test-junit4")
    debugImplementation("androidx.compose.ui:ui-test-manifest")
}

// BROKE on AGP 7.2+
android {
    sourceSets {
        getByName("test").java.srcDir("src/sharedTest/java")
        getByName("androidTest").java.srcDir("src/sharedTest/java")
    }
}

// MIGRATION OPTION A — extract a :core-testing sub-module
// :core-testing/build.gradle.kts
plugins { id("java-library") }
// classes here are consumed by both test sourcesets in dependent modules

// :feature:home/build.gradle.kts
dependencies {
    testImplementation(project(":core-testing"))
    androidTestImplementation(project(":core-testing"))
}

// MIGRATION OPTION B — testFixtures
android {
    testFixtures { enable = true }
}
// src/testFixtures/java/...    contains FakeUserRepository, MainDispatcherRule

// dependent module
dependencies {
    testImplementation(testFixtures(project(":core")))
    androidTestImplementation(testFixtures(project(":core")))
}

// MIGRATION OPTION C — KMP source-set naming
// In a KMP Android module:
kotlin {
    androidTarget {
        compilations.getByName("debug") { /* ... */ }
    }
    sourceSets {
        val androidHostTest by getting          // Robolectric, JVM
        val androidDeviceTest by getting        // emulator/device
        val androidCommonTest by getting        // helpers shared by both
        androidHostTest.dependsOn(androidCommonTest)
        androidDeviceTest.dependsOn(androidCommonTest)
    }
}

plugins {
    id("com.android.library")
    id("org.jetbrains.kotlin.android")
}

android {
    namespace = "com.example.feature.home"
    compileSdk = 35
    defaultConfig {
        minSdk = 23
        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }
    testOptions {
        unitTests.isIncludeAndroidResources = true   // required for Robolectric
        animationsDisabled = true                    // hermetic instrumented tests
    }
}

dependencies {
    // production
    implementation("androidx.activity:activity-compose")

    // host (JVM) tests — src/test/
    testImplementation("junit:junit:4.13.2")
    testImplementation("androidx.test:core:1.7.0")
    testImplementation("androidx.test.ext:junit:1.3.0")
    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.10.0")
    testImplementation("org.mockito:mockito-core:5.13.0")
    testImplementation("org.mockito.kotlin:mockito-kotlin:5.4.0")
    testImplementation("org.robolectric:robolectric:4.13")
    testImplementation("app.cash.turbine:turbine:1.1.0")

    // instrumented (device) tests — src/androidTest/
    androidTestImplementation("androidx.test.ext:junit:1.3.0")
    androidTestImplementation("androidx.test.espresso:espresso-core:3.7.0")
    androidTestImplementation("androidx.compose.ui:ui-test-junit4")

    // debug-only — merged manifest entries for test scaffolds
    debugImplementation("androidx.compose.ui:ui-test-manifest")
    debugImplementation("androidx.fragment:fragment-testing-manifest:1.8.5")

    // orchestrator (note: androidTestUtil, not androidTestImplementation)
    androidTestUtil("androidx.test:orchestrator:1.6.1")
}