Delegate runner 'androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner' for AndroidJUnit4 could not be loaded

I faced this problem in kotlin , used below code and it worked

@RunWith(AndroidJUnit4::class)

@LargeTest

class MainActivityTest {

    private val TAG = "MainActivityTest"

    @get:Rule
    val activityRule = ActivityTestRule(MainActivity::class.java)
}

follow the link below:- https://developer.android.com/training/testing/junit-rules

The error message displayed when I delete the @Test method.

You can try to put a @Test method and run

@Test
public void signInTest() {


}

For those who still have problems like this, This happens because Kotlin compiler wants to generate getter/setter properties. for example, I've got this error because I didn't mention @Rule annotation with @get:Rule.

If we annotate properties like this with @get:... or @JvmField it could solve the problem.

@get:Rule
var mActivityRule = ActivityTestRule(MainActivity::class.java)

Or

@Rule
@JvmField
var mActivityRule = ActivityTestRule(MainActivity::class.java)

@JvmField instructs the Kotlin compiler not to generate getters/setters for this property and expose it as a field.

In regards to @RunWith(AndroidJUnit4::class)

Delete

import androidx.test.ext.junit.runners.AndroidJUnit4

Use

import androidx.test.runner.AndroidJUnit4

I got this error when I have some parameters in my test method. So, if you have it - delete it.

@Test
fun someTestMethod(someParams: Int) { // delete method params
    assert(1==1)
}

just make sure that if your test is calling any suspend methods, you run your test with runBlocking{}. Solved the problem for me

Max Kilzieh answer worked for me Using import androidx.test.runner.AndroidJUnit4 instead of import androidx.test.ext.junit.runners.AndroidJUnit4

I just wasted all day on this issue 😵

I'm guessing you are using the multiplatform plugin like I am.

I was about to give up on trying to moving my instrumented tests to src/androidTest/kotlin instead of src/androidTest/java

when I decided to log kotlin.sourcesets.names, which printed

[androidAndroidTest, androidAndroidTestDebug, androidDebug, androidMain, androidRelease, androidTest, androidTestDebug, androidTestRelease, commonMain, commonTest, iosArm32Main, iosArm32Test, iosArm64Main, iosArm64Test, iosX64Main, iosX64Test, macosX64Main, macosX64Test]

Soo I realized in order for dependencies to resolve correctly I needed to change

androidTestImplementation -> androidAndroidTestImplementation
testImplementation -> androidTestImplementation

They don't describe this in the documentation of course. (as far as I have found)

... so for example, for you, I think the dependencies for your instrumented test dependencies should be:

androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0-alpha02'

not

androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0-alpha02'

You don't have any functions annotated with @Test. This is likely the cause of the issue. I've run my own test using the AndroidJUnit4 runner on a class without @Test functions, and reconstructed this behavior.

The AndroidJUnit4 JUnit4 runner is the cause of this issue, and despite its attempt to provide a detailed message (see the code where the exception is thrown), it gives you a wrong message.

The following are more ways to achieve this error:

@Test
fun willThrowInitializationErrorBecauseReturnsNonUnitValue(): Int {
    return 0
}

@Test
fun willThrowInitializationErrorBecauseTakesParameters(param: Int) {
}

The error is generated by the fact that you're writing JUnit4 style tests, and they're expected to conform to JUnit4 semantics, but it would be nice if the error message were more clear.

To make matters worse, if one test function is messed up the runner won't run any tests because the InitializationError is thrown in the constructor of the AndroidJUnit4 class.

In My case while using Java,I faced issue when I did below mistakes.

1)I had made ActivityTestRule as private.

  All test cases should be public always.

2)I didn't add static for BeforeClass and AfterClass methods

  Methods of @BeforeClass and @AfterClass should be static

  Ex)@BeforeClass
     public static void setUp(){

     }

Also just to expand on the answers, but it won't help for this particular reason:

If you use kotlin and get this while testing, make sure you aren't using suspend in DAO.

(Sorry to put it here, there was no thread with this in kotlin and I already found the solution so it might help someone)