title: Espresso Test : app:compileDebugAndroidTestKotlin FAILED with Unresolved reference: PopupBackgroundView
body: <p>I recorded an EspressoTest in which I test values in spinner :</p>
  <pre><code>&lt;LinearLayout
      android:id=&quot;@+id/linearLayoutSeedlingsTypes&quot;
      android:layout_width=&quot;wrap_content&quot;
      android:layout_height=&quot;wrap_content&quot;
      android:layout_marginTop=&quot;40dp&quot;&gt;
      &lt;androidx.cardview.widget.CardView
          android:layout_width=&quot;180dp&quot;
          android:layout_height=&quot;wrap_content&quot;
          app:cardCornerRadius=&quot;20dp&quot;
          android:innerRadius=&quot;0dp&quot;
          android:shape=&quot;ring&quot;
          android:thicknessRatio=&quot;1.9&quot;
          android:backgroundTint=&quot;@color/green&quot;
          android:background=&quot;@color/green&quot;&gt;
          &lt;Spinner
              android:id=&quot;@+id/fas_spinner_types&quot;
              android:layout_width=&quot;match_parent&quot;
              android:layout_height=&quot;30dp&quot;
              android:layout_marginLeft=&quot;@dimen/default_margin&quot;
              android:layout_marginStart=&quot;@dimen/default_margin&quot;
              android:entries=&quot;@array/seedlings_types&quot;
              android:spinnerMode=&quot;dropdown&quot;
              /&gt;
  </code></pre>
  <p>It generated the following Kotlin class :</p>
  <pre><code>@LargeTest
  @RunWith(AndroidJUnit4::class)
  class AddNominalTest {
  
      @Rule
      @JvmField
      var mActivityTestRule = ActivityTestRule(MainActivity::class.java)
  
      @Test
      fun addNominal() {
              //...
              
              val materialTextView = onData(anything())
              .inAdapterView(
                  childAtPosition(
                      withClassName(`is`(&quot;android.widget.PopupWindow$PopupBackgroundView&quot;)),//compile error !
                      0
                  )
              )
              .atPosition(1)
          materialTextView.perform(click())
          
          //...
      
  </code></pre>
  <p>I have the following error at compile in <strong>app:compileDebugAndroidTestKotlin : Unresolved reference: PopupBackgroundView</strong></p>
  <p>Any idea about this error ?</p>