title: Unresolved reference ActivityTestRule for AndroidX
body: <p>I'm trying to test my UI via instrumentation test, with androidX espresso library.
  In my grade I have:</p>
  
  <pre class="lang-kotlin prettyprint-override"><code>apply plugin: 'com.android.application'
  
  apply plugin: 'kotlin-android'
  
  apply plugin: 'kotlin-android-extensions'
  apply plugin: "kotlin-kapt"
  
  android {
      compileSdkVersion 28
      defaultConfig {
          applicationId "it.zehus.mybike"
          minSdkVersion 21
          targetSdkVersion 28
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
          android.defaultConfig.manifestPlaceholders = ['appAuthRedirectScheme': 'net.openid.appauthdemo']
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      implementation fileTree(dir: 'libs', include: ['*.jar'])
  
      def lifecycle_version = "2.0.0"
      // ViewModel and LiveData
      implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"
  
      // room persistence library
      def room_version = "2.1.0-alpha04"
      implementation "androidx.room:room-runtime:$room_version"
      kapt "androidx.room:room-compiler:$room_version" // use kapt for Kotlin
      // optional - Coroutines support for Room
      implementation "androidx.room:room-coroutines:$room_version"
  
      implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
      implementation 'androidx.appcompat:appcompat:1.0.2'
      implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
      implementation 'com.google.android.material:material:1.0.0'
  
      // Espresso
      androidTestImplementation 'androidx.test:runner:1.1.0'
      androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0'
      implementation project(path: ':remotemanager')
      implementation "org.jetbrains.kotlin:kotlin-reflect:1.3.21"
  
      androidTestImplementation 'androidx.test.ext:junit:1.1.0'
      // required if you want to use Mockito for unit tests
      testImplementation 'org.mockito:mockito-core:2.24.5'
      // required if you want to use Mockito for Android tests
      androidTestImplementation 'org.mockito:mockito-android:2.24.5'
      // Bluetooth sdk
      implementation project(path: ':bluetoothmanager')
      // Custom views
      implementation project(path: ':customviews')
  
  
  }
  </code></pre>
  
  <p>As specified in the <a href="https://developer.android.com/training/testing/ui-testing/espresso-testing.html" rel="noreferrer">documentation</a> I'm attempting to import ActivityTestRule class in my test, however the reference is unresolved.</p>
  
  <pre class="lang-kotlin prettyprint-override"><code>import androidx.test.filters.LargeTest
  import androidx.test.runner.AndroidJUnit4
  import org.junit.Rule
  import org.junit.Test
  import org.junit.runner.RunWith
  // unresolved reference here
  import androidx.test.rule.ActivityTestRule
  import it.zehus.mybike.ui.ride.RideActivity
  
  
  /**
   * Instrumented test, which will execute on an Android device.
   *
   * See [testing documentation](http://d.android.com/tools/testing).
   */
  // deprecated here
  @RunWith(AndroidJUnit4::class)
  @LargeTest
  class FragmentDashboardUiTest {
      @get:Rule // unresolved reference here
      val activityRule = ActivityTestRule(RideActivity::class.java)
  
      @Test
      fun myClassMethod_ReturnsTrue() {  }
  }
  </code></pre>
  
  <p>Am I doing something wrong or there's a problem within AndroidX testing libraries?</p>