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

Question

I try to run Kotlin instrumentation tests for android.

In my app/build.gradle:

    android {
        dataBinding {
            enabled = true
               


        

Answer 1

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(){

     }

Answer 2

I just wasted all day on this issue

Answer 3

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.

Answer 4

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.

Answer 5

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

You can try to put a @Test method and run

@Test
public void signInTest() {


}

Answer 6

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