Android Instrumentation Testing: No instrumentation registered Error

I am trying to write Android Instrumented test using Espresso. When I run the test I get this error

java.lang.IllegalStateException: No instrumentation registered! Must run under a registering instrumentation.

I can’t understand what this error means.

I will briefly explain what I am doing in my test. I followed the samples given by google and EspressoTesting Tutorial

@SmallTest
@RunWith(AndroidJUnit4.class)
public class ActivityInputTest {

   @Rule
   public ActivityTestRule<ActivityInput> aiRule = new ActivityTestRule<>(ActivityInput.class);


   @Before
   public void setUp(){}
}

When I run the test the error occurs at annotation @Rule. Can I get some explanation why this happens or what is the issue behind this? I am not interested in working code but more on the actual problem behind the issue.

Answer

I also experienced error exactly same with you, because I used androidx library. I suggest you to check your libraries in build.gradle and change your dependencies for UI test like these block codes:

androidTestImplementation "com.android.support.test:runner:1.0.2"
androidTestImplementation "com.android.support.test:rules:1.0.2"
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

Choose one of them, using com.android.support.test, or androidx library, because if we use them together, they will conflict each other. Hope this can help you to resolve error No instrumentation registered! Must run under a registering instrumentation.

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