Delegate runner 'org.robolectric.RobolectricTestRunner' for AndroidJUnit4 could not be loaded.

Description

I am trying to use ActivityScenarioRule in my jUnit tests. However, if I add it to my test it gives me the exception as shown below.

Steps to Reproduce

• Create a new project with Android Studio 3.4
• Update the build.gradle file with the following dependencies:

 dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    testImplementation "androidx.test:core:1.1.1"
    testImplementation "androidx.test.ext:junit:1.1.1"
    testImplementation "org.robolectric:robolectric:4.2.1"
    androidTestImplementation "androidx.test:runner:1.1.1"
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

• Update the existing unit test like this:

import androidx.test.ext.junit.rules.ActivityScenarioRule;
import androidx.test.ext.junit.runners.AndroidJUnit4;

import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;

import static org.junit.Assert.*;

/**
 * Example local unit test, which will execute on the development machine (host).
 *
 * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
 */
@RunWith(AndroidJUnit4.class)
public class ExampleUnitTest {

    @Rule
    ActivityScenarioRule<MainActivity> activityScenarioRule = new ActivityScenarioRule<>(MainActivity.class);

    @Test
    public void addition_isCorrect() {
        assertEquals(4, 2 + 2);
    }
}

• Run the test

Expected Results

The test should pass

Actual Results

The following exception is thrown:

java.lang.RuntimeException: Delegate runner 'org.robolectric.RobolectricTestRunner' for AndroidJUnit4 could not be loaded.

	at androidx.test.ext.junit.runners.AndroidJUnit4.throwInitializationError(AndroidJUnit4.java:92)
	at androidx.test.ext.junit.runners.AndroidJUnit4.loadRunner(AndroidJUnit4.java:82)
	at androidx.test.ext.junit.runners.AndroidJUnit4.loadRunner(AndroidJUnit4.java:51)
	at androidx.test.ext.junit.runners.AndroidJUnit4.<init>(AndroidJUnit4.java:46)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at org.junit.internal.builders.AnnotatedBuilder.buildRunner(AnnotatedBuilder.java:104)
	at org.junit.internal.builders.AnnotatedBuilder.runnerForClass(AnnotatedBuilder.java:86)
	at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59)
	at org.junit.internal.builders.AllDefaultPossibilitiesBuilder.runnerForClass(AllDefaultPossibilitiesBuilder.java:26)
	at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59)
	at org.junit.internal.requests.ClassRequest.getRunner(ClassRequest.java:33)
	at org.junit.internal.requests.FilterRequest.getRunner(FilterRequest.java:36)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:49)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at androidx.test.ext.junit.runners.AndroidJUnit4.loadRunner(AndroidJUnit4.java:72)
	... 17 more
Caused by: org.junit.runners.model.InitializationError
	at org.junit.runners.ParentRunner.validate(ParentRunner.java:418)
	at org.junit.runners.ParentRunner.<init>(ParentRunner.java:84)
	at org.junit.runners.BlockJUnit4ClassRunner.<init>(BlockJUnit4ClassRunner.java:65)
	at org.robolectric.internal.SandboxTestRunner.<init>(SandboxTestRunner.java:75)
	at org.robolectric.RobolectricTestRunner.<init>(RobolectricTestRunner.java:100)
	at org.robolectric.RobolectricTestRunner.<init>(RobolectricTestRunner.java:95)
	... 22 more

AndroidX Test and Android OS Versions

    testImplementation 'junit:junit:4.12'
    testImplementation "androidx.test:core:1.1.1"
    testImplementation "androidx.test.ext:junit:1.1.1"
    testImplementation "org.robolectric:robolectric:4.2.1"
    androidTestImplementation 'androidx.test:runner:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

    Android Studio 3.4
    Windows 10

Link to a public git repo demonstrating the problem:

DemoActivityScenarioRule

If I comment the ActivityScenarioRule, the test pass without problems.

[ajharry69]

Make sure you have at least one test method in your class before trying to run the test class(Could also be relevant in some scenario)

[rajBopche]

I encountered the same error when my setUp() method annotated with @Before was private. The fix was to remove the private modifier.