title: Delegate runner 'androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner' for AndroidJUnit4 could not be loaded
body: <p>I  try to run Kotlin instrumentation tests for android.</p>
  
  <p>In my app/build.gradle:</p>
  
  <pre><code>    android {
          dataBinding {
              enabled = true
          }
          compileSdkVersion 28
          defaultConfig {
              applicationId "com.myproject"
              minSdkVersion 18
              targetSdkVersion 28
              versionCode 6
              versionName "0.0.7"
              testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
          }
  
          sourceSets {
              main.java.srcDirs += 'src/main/kotlin'
              androidTest.java.srcDirs += 'src/androidTest/kotlin'
          }
  
  androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0-alpha02'
      androidTestImplementation 'androidx.test.ext:junit:1.1.0'
      androidTestImplementation 'androidx.test:rules:1.1.2-alpha02'
      androidTestImplementation 'androidx.test:runner:1.1.2-alpha02'
  </code></pre>
  
  <p>In folder <code>/app/src/androidTest/kotlin/com/myproject/</code>  I has Kotlin test:</p>
  
  <pre><code>import androidx.test.ext.junit.runners.AndroidJUnit4
  import androidx.test.filters.SmallTest
  import org.junit.Rule
  import org.junit.runner.RunWith
  
  import androidx.test.rule.ActivityTestRule
  import com.myproject.ui.activity.TradersActivity
  import org.junit.Before
  
  
  @RunWith(AndroidJUnit4::class)
  @SmallTest
  class TradersActivityTest {
  
      private lateinit var stringToBetyped: String
  
      @get:Rule
      var activityRule: ActivityTestRule&lt;TradersActivity&gt; = ActivityTestRule(TradersActivity::class.java)
  
      @Before
      fun initValidString() {
          // Specify a valid string.
          stringToBetyped = "Espresso"
      }
  
  }
  </code></pre>
  
  <p>but when I run test I get error:</p>
  
  <pre><code>$ adb shell am instrument -w -r   -e debug false -e class 'com.myproject.TradersActivityTest' com.myproject.debug.test/androidx.test.runner.AndroidJUnitRunner
  Client not ready yet..
  Started running tests
  
  java.lang.RuntimeException: Delegate runner 'androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner' 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.&lt;init&gt;(AndroidJUnit4.java:46)
  at java.lang.reflect.Constructor.newInstance(Native Method)
  at org.junit.internal.builders.AnnotatedBuilder.buildRunner(AnnotatedBuilder.java:104)
  at org.junit.internal.builders.AnnotatedBuilder.runnerForClass(AnnotatedBuilder.java:86)
  at androidx.test.internal.runner.junit4.AndroidAnnotatedBuilder.runnerForClass(AndroidAnnotatedBuilder.java:63)
  at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59)
  at org.junit.internal.builders.AllDefaultPossibilitiesBuilder.runnerForClass(AllDefaultPossibilitiesBuilder.java:26)
  at androidx.test.internal.runner.AndroidRunnerBuilder.runnerForClass(AndroidRunnerBuilder.java:153)
  at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59)
  at androidx.test.internal.runner.TestLoader.doCreateRunner(TestLoader.java:73)
  at androidx.test.internal.runner.TestLoader.getRunnersFor(TestLoader.java:104)
  at androidx.test.internal.runner.TestRequestBuilder.build(TestRequestBuilder.java:789)
  at androidx.test.runner.AndroidJUnitRunner.buildRequest(AndroidJUnitRunner.java:544)
  at androidx.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:387)
  at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1879)
  Caused by: java.lang.reflect.InvocationTargetException
  at java.lang.reflect.Constructor.newInstance(Native Method)
  at androidx.test.ext.junit.runners.AndroidJUnit4.loadRunner(AndroidJUnit4.java:72)
  ... 16 more
  Caused by: org.junit.runners.model.InitializationError
  at org.junit.runners.ParentRunner.validate(ParentRunner.java:418)
  at org.junit.runners.ParentRunner.&lt;init&gt;(ParentRunner.java:84)
  at org.junit.runners.BlockJUnit4ClassRunner.&lt;init&gt;(BlockJUnit4ClassRunner.java:65)
  at androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner.&lt;init&gt;(AndroidJUnit4ClassRunner.java:43)
  at androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner.&lt;init&gt;(AndroidJUnit4ClassRunner.java:48)
  ... 18 more
  
  Tests ran to completion.
  </code></pre>