Configuring Junit4 On Android

Configuring JUnit4 on Android — The Right Runner, Registry, and Matrix

Almost every "test suite is misconfigured" report boils down to one of three root causes: the wrong AndroidJUnit4 is imported, the wrong InstrumentationRegistry is imported, or the size-annotation / dispatcher plumbing is missing. This skill encodes the exact Gradle matrix from androidx.test:core 1.7.0 onward, the canonical FQCNs, and the minimal MainDispatcherRule pattern that androidx itself ships in testutils-ktx.

When to use this skill

• The user reports Cannot resolve symbol AndroidJUnit4, AndroidJUnit4 is deprecated, or asks "which AndroidJUnit4 should I import".
• The user reports IllegalStateException: No instrumentation registered from InstrumentationRegistry.getInstrumentation() in a unit test, or asks why InstrumentationRegistry is crossed out.
• The user wants Truth subjects (IntentSubject, BundleSubject, LocationSubject, ParcelableSubject) but does not know which artifact ships them.
• The user wants am instrument -e size small to filter tests and asks how to wire @SmallTest / @MediumTest / @LargeTest.
• The user is writing a ViewModel / coroutine test and needs the canonical MainDispatcherRule template.

When NOT to use this skill

• The user is wiring Mockito mocks — use ../../mocking/mocking-with-mockito/SKILL.md.
• The user is wiring MockK mocks — use ../../mocking/mocking-with-mockk/SKILL.md.
• The user is configuring runTest { … } or Turbine — use ../../coroutines/testing-coroutines-with-runtest/SKILL.md or ../../coroutines/testing-flows-with-turbine/SKILL.md.
• The user is configuring Robolectric specifically (SDK matrix, resources, @Config) — use ../../robolectric/using-robolectric-correctly/SKILL.md.
• The user is running tests on a device with am instrument — use ../../../instrumentation/runner/running-instrumented-tests-with-androidjunit4/SKILL.md.
• The user is choosing between fakes and mocks — use ../../../fundamentals/doubles/picking-test-doubles/SKILL.md.

Prerequisites

• Android Gradle Plugin applied (com.android.application or com.android.library).
• A src/test/ source set on disk (Gradle creates it lazily — mkdir -p src/test/kotlin if missing).
• Kotlin module (these notes assume Kotlin; the same FQCNs work from Java).
• For coroutine-related tests, org.jetbrains.kotlinx:kotlinx-coroutines-test:1.10.x already on the classpath.

Workflow

• 1. Pin the canonical Gradle dependency matrix. These are the released stable versions backing this skill (verified against ~/.gradle/caches/modules-2/files-2.1/androidx.test/...). Pin them directly, do not latest.release:

dependencies {
    // Core JUnit4
    testImplementation("junit:junit:4.13.2")

    // androidx.test foundations (work in src/test/ via Robolectric and in src/androidTest/)
    testImplementation("androidx.test:core:1.7.0")
    testImplementation("androidx.test:core-ktx:1.6.1")
    testImplementation("androidx.test:runner:1.7.0")
    testImplementation("androidx.test:rules:1.7.0")
    testImplementation("androidx.test.ext:junit:1.3.0")
    testImplementation("androidx.test.ext:junit-ktx:1.3.0")
    testImplementation("androidx.test.ext:truth:1.7.0")
    testImplementation("com.google.truth:truth:1.4.4")

    // Coroutines test (for MainDispatcherRule / runTest)
    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.10.1")
}

For instrumented tests in src/androidTest/, mirror the same artifacts on androidTestImplementation. The artifacts are dual-classpath compatible.

• 2. Annotate test classes with the correct @RunWith. There are TWO classes named AndroidJUnit4 on the classpath. The deprecated one is androidx.test.runner.AndroidJUnit4 (file runner-1.7.0/androidx/test/runner/AndroidJUnit4.java L41-44 — @Deprecated). The canonical one is androidx.test.ext.junit.runners.AndroidJUnit4 from the androidx.test.ext:junit:1.3.0 artifact (file junit-1.3.0/androidx/test/ext/junit/runners/AndroidJUnit4.java L49). It delegates to Robolectric on the JVM (when org.robolectric.RobolectricTestRunner is on the classpath) and to androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner on a device.

import androidx.test.ext.junit.runners.AndroidJUnit4   // canonical
import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)
class MyTest { /* ... */ }

• 3. Use the canonical InstrumentationRegistry. androidx.test.InstrumentationRegistry (no .platform.app.) is @Deprecated since :monitor 1.x — every member is @InlineMe'd to its replacement. The canonical class is androidx.test.platform.app.InstrumentationRegistry (file monitor-1.8.0/androidx/test/platform/app/InstrumentationRegistry.java L30-85).

import androidx.test.platform.app.InstrumentationRegistry

val instrumentation = InstrumentationRegistry.getInstrumentation()
val args: Bundle = InstrumentationRegistry.getArguments()  // copy of -e key/value pairs

getInstrumentation() throws IllegalStateException("No instrumentation registered! Must run under a registering instrumentation.") if called outside an instrumentation host or before Robolectric initialises its shadow. Robolectric registers an Instrumentation instance into the registry before tests run, so this works in src/test/ when @RunWith(AndroidJUnit4::class) is in effect.

• 4. Pull the application Context via ApplicationProvider, not via the registry. ApplicationProvider.getApplicationContext() is the single entry point for the Application context (file core-1.7.0/androidx/test/core/app/ApplicationProvider.java L29-43). Internally it returns getInstrumentation().getTargetContext().getApplicationContext() — same Context, more readable callsite, and the unchecked generic lets callers cast to their Application subclass.

import androidx.test.core.app.ApplicationProvider

val ctx: Context = ApplicationProvider.getApplicationContext()
val app: MyApp = ApplicationProvider.getApplicationContext()   // unchecked cast

• 5. Tag each test with a size annotation when the suite is large enough to need filtering. Size is one of three: @SmallTest (<200ms, no Android stubs), @MediumTest (<1000ms, Android framework via Robolectric), @LargeTest (>1000ms, instrumented). Annotations live in androidx.test.filters.* (file runner-1.7.0/androidx/test/filters/SmallTest.java L44-46). The runner's RunnerArgs.SIZE (runner-1.7.0/androidx/test/internal/runner/RunnerArgs.java L58) wires -e size <value> directly to these annotations.

import androidx.test.filters.SmallTest
import androidx.test.filters.MediumTest

@SmallTest
class FastValidatorTest { /* ... */ }

@MediumTest
class RoomDaoTest { /* ... */ }

The corresponding am instrument invocation is adb shell am instrument -w -r -e size small <pkg>/androidx.test.runner.AndroidJUnitRunner. See ../../../instrumentation/runner/running-instrumented-tests-with-androidjunit4/SKILL.md for the on-device counterpart.

• 6. Reach for Truth subjects from androidx.test.ext:truth for Android-domain assertions. Truth shipped with androidx.test.ext:truth:1.7.0 adds Android-aware Subject types. Each exposes a static assertThat(T actual) shortcut and a static Subject.Factory<T, S> name() factory:

Idiomatic import-and-call:

import androidx.test.ext.truth.content.IntentSubject.assertThat
import androidx.test.ext.truth.os.BundleSubject

@Test fun intent_routes_to_settings() {
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("settings://wifi"))
    assertThat(intent).hasAction(Intent.ACTION_VIEW)
    assertThat(intent).hasData(Uri.parse("settings://wifi"))
}

• 7. Install a MainDispatcherRule for any test that touches Dispatchers.Main. Compose, viewModelScope, and LiveData all default to Dispatchers.Main, which is unavailable on the JVM unless swapped. The canonical androidx pattern lives at testutils/testutils-ktx/src/jvmMain/kotlin/androidx/testutils/MainDispatcherRule.jvm.kt — use it verbatim:

import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.test.StandardTestDispatcher
import kotlinx.coroutines.test.TestDispatcher
import kotlinx.coroutines.test.resetMain
import kotlinx.coroutines.test.setMain
import org.junit.rules.TestWatcher
import org.junit.runner.Description

@OptIn(ExperimentalCoroutinesApi::class)
class MainDispatcherRule(
    val testDispatcher: TestDispatcher = StandardTestDispatcher(),
) : TestWatcher() {
    override fun starting(description: Description) {
        Dispatchers.setMain(testDispatcher)
    }

    override fun finished(description: Description) {
        Dispatchers.resetMain()
    }
}

Apply on a test class:

@RunWith(AndroidJUnit4::class)
class MyViewModelTest {
    @get:Rule val mainDispatcherRule = MainDispatcherRule()

    @Test fun loadsUsers() = runTest {
        val vm = MyViewModel(repo = FakeUserRepository())
        vm.load()
        advanceUntilIdle()
        assertThat(vm.users.value).isNotEmpty()
    }
}

StandardTestDispatcher is preferred — it queues continuations and only advances on runCurrent()/advanceUntilIdle(), matching kotlinx.coroutines.test.runTest semantics. UnconfinedTestDispatcher dispatches eagerly and is appropriate only when ordering is irrelevant.

• 8. Verify the test class actually runs. Execute the suite once: ./gradlew :<module>:testDebugUnitTest --tests com.example.MyTest. The Gradle output shows the runner choice — org.junit.runner.RunWith: AndroidJUnit4 confirms the canonical runner is bound; Test process exited with status code near the top confirms Robolectric is wiring up.

Patterns

Pattern: WRONG vs RIGHT — choosing the AndroidJUnit4 runner

// WRONG
import org.junit.runners.JUnit4
import org.junit.runner.RunWith

@RunWith(JUnit4::class)
class MyTest { /* uses InstrumentationRegistry, ApplicationProvider, ... */ }
// WRONG because: stock JUnit4 does not register the Android `Instrumentation` instance
// into InstrumentationRegistry. ApplicationProvider.getApplicationContext() throws
// IllegalStateException("No instrumentation registered!"). Robolectric is also never
// activated even when on the classpath, so all framework calls hit unmocked stubs.

// RIGHT
import androidx.test.ext.junit.runners.AndroidJUnit4   // ext.junit.runners, NOT runner.AndroidJUnit4
import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)
class MyTest { /* ... */ }

The deprecated alias androidx.test.runner.AndroidJUnit4 still compiles but emits an unsuppressed deprecation warning. New code MUST import from androidx.test.ext.junit.runners.

Pattern: WRONG vs RIGHT — InstrumentationRegistry import

// WRONG
import androidx.test.InstrumentationRegistry        // @Deprecated since :monitor

val ctx = InstrumentationRegistry.getContext()      // also deprecated — not the Application context
// WRONG because: every member of androidx.test.InstrumentationRegistry is @Deprecated
// and @InlineMe'd to its replacement. getContext() returns the instrumentation package
// context, NOT the Application context — common source of "resource not found" failures.

// RIGHT
import androidx.test.platform.app.InstrumentationRegistry
import androidx.test.core.app.ApplicationProvider

val ctx: Context = ApplicationProvider.getApplicationContext()    // application context
val args: Bundle = InstrumentationRegistry.getArguments()          // -e key/value pairs
val instr = InstrumentationRegistry.getInstrumentation()

Pattern: WRONG vs RIGHT — accessing Compose Dispatchers.Main from a unit test

// WRONG
class MyViewModelTest {
    @Test fun loadsUsers() = runBlocking {
        val vm = MyViewModel(repo = FakeUserRepository())
        vm.load()
        // Throws IllegalStateException: "Module with the Main dispatcher is missing"
    }
}
// WRONG because: kotlinx-coroutines-android (the Main dispatcher impl for Android) is
// NOT on the unit-test classpath. Without Dispatchers.setMain(...), any viewModelScope or
// LaunchedEffect that touches the Main dispatcher fails immediately.

// RIGHT
class MyViewModelTest {
    @get:Rule val mainDispatcherRule = MainDispatcherRule()

    @Test fun loadsUsers() = runTest {
        val vm = MyViewModel(repo = FakeUserRepository())
        vm.load()
        advanceUntilIdle()
        assertThat(vm.users.value).hasSize(2)
    }
}

Pattern: filtering by size from the command line

The @SmallTest / @MediumTest / @LargeTest annotations bind directly to RunnerArgs.SIZE (runner-1.7.0/androidx/test/internal/runner/RunnerArgs.java L58). For instrumented tests:

adb shell am instrument -w -r -e size small \
    com.example.test/androidx.test.runner.AndroidJUnitRunner

For Robolectric-on-JVM tests, Gradle property filtering is the standard route:

./gradlew :app:testDebugUnitTest --tests "com.example.*" \
    -PandroidTestSize=small

Combined with -e annotation com.example.SmokeTest (the RunnerArgs.ANNOTATION arg, L60) you get composable filtering.

Mandatory rules

• MUST import AndroidJUnit4 from androidx.test.ext.junit.runners. MUST NOT import androidx.test.runner.AndroidJUnit4 — it is @Deprecated.
• MUST import InstrumentationRegistry from androidx.test.platform.app. MUST NOT import androidx.test.InstrumentationRegistry — it is @Deprecated.
• MUST use ApplicationProvider.getApplicationContext() for the Application context. MUST NOT call InstrumentationRegistry.getInstrumentation().getTargetContext() directly — ApplicationProvider is the canonical entry point and handles the unchecked cast.
• MUST install a MainDispatcherRule (or equivalent Dispatchers.setMain/resetMain plumbing) before any test that touches viewModelScope, LaunchedEffect, or any Dispatchers.Main consumer. Without it, the test crashes with IllegalStateException: Module with the Main dispatcher is missing.
• MUST prefer StandardTestDispatcher over UnconfinedTestDispatcher in MainDispatcherRule. StandardTestDispatcher matches runTest semantics; eager dispatch is a footgun for ordering.
• MUST annotate every test class or method with exactly ONE size annotation (@SmallTest / @MediumTest / @LargeTest) when the suite is filtered by size. Multiple size annotations on the same target produce undefined runner behaviour.
• MUST pin Robolectric independently — it does not ship in the androidx-test BOM. Use org.robolectric:robolectric:4.x matching the compileSdk of the module.
• MUST NOT use runBlockingTest { } in new code — it is @Deprecated(level = DeprecationLevel.ERROR) since kotlinx-coroutines-test 1.7. Use runTest { } instead.
• MUST NOT use ActivityTestRule<A> — it is @Deprecated. Use androidx.test.ext.junit.rules.ActivityScenarioRule<A> instead (junit-1.3.0/androidx/test/ext/junit/rules/ActivityScenarioRule.java L56). For instrumented variants, see ../../../instrumentation/runner/running-instrumented-tests-with-androidjunit4/SKILL.md.
• PREFERRED: declare testOptions.unitTests.isIncludeAndroidResources = true in the module's android { … } block. Robolectric needs merged resources to inflate any layout or read R.string.*.

Verification

• ./gradlew :<module>:testDebugUnitTest compiles and reports Tests run: N, Failures: 0 for the new suite.
• grep -r "import androidx.test.runner.AndroidJUnit4" src/test src/androidTest returns NO matches (only androidx.test.ext.junit.runners.AndroidJUnit4 is allowed).
• grep -r "import androidx.test.InstrumentationRegistry" src/test src/androidTest returns NO matches.
• Any test that uses viewModelScope / Dispatchers.Main declares @get:Rule val mainDispatcherRule = MainDispatcherRule() and uses runTest { … }.
• At least one test class is annotated with @SmallTest, @MediumTest, or @LargeTest if the suite is meant to be filtered.
• ./gradlew :<module>:testDebugUnitTest --info output shows org.robolectric.RobolectricTestRunner (host) or AndroidJUnit4ClassRunner (device) in the runner stack — confirming the AndroidJUnit4 delegate selection.

References

• AndroidX Test releases: https://developer.android.com/jetpack/androidx/releases/test
• Local tests guide: https://developer.android.com/training/testing/local-tests
• Instrumented tests guide: https://developer.android.com/training/testing/instrumented-tests
• AndroidJUnitRunner reference: https://developer.android.com/training/testing/junit-runner
• Truth subject reference (upstream tree): https://github.com/android/android-test/tree/main/ext/truth/java/androidx/test/ext/truth
• runner-1.7.0/androidx/test/runner/AndroidJUnit4.java (L41-44) — @Deprecated alias.
• junit-1.3.0/androidx/test/ext/junit/runners/AndroidJUnit4.java (L49-70) — canonical runner with Robolectric/Android delegate selection.
• monitor-1.8.0/androidx/test/platform/app/InstrumentationRegistry.java (L30-85) — canonical registry; getInstrumentation, getArguments, registerInstance.
• monitor-1.8.0/androidx/test/InstrumentationRegistry.java (L34) — @Deprecated legacy registry.
• core-1.7.0/androidx/test/core/app/ApplicationProvider.java (L29-43) — single-method facade returning the Application context.
• runner-1.7.0/androidx/test/filters/SmallTest.java (L44-46), MediumTest.java, LargeTest.java — size annotation definitions.
• runner-1.7.0/androidx/test/internal/runner/RunnerArgs.java (L54-99) — every -e <key> <value> argument the runner accepts, including size, annotation, class, package, numShards/shardIndex.
• testutils/testutils-ktx/src/jvmMain/kotlin/androidx/testutils/MainDispatcherRule.jvm.kt — canonical androidx MainDispatcherRule source, identical pattern shipped here.
• Cross-set: ../../../kotlin/kotlin-test/writing-tests-with-kotlin-test/SKILL.md — the framework-agnostic kotlin.test assertions (assertEquals, assertFailsWith, @BeforeTest) used inside these JUnit4 tests; also the only assertion API available in commonTest.