Migrate frameworks/base/tests/testables and its users to androidx.test

See go/jetpack-test-android-migration

Test: atest TestablesTests NetworkStackTests FrameworksServicesTests SystemUITests FrameworksUiServicesTests ExtServicesUnitTests
Exempt-From-Owner-Approval: already reviewed
Change-Id: I083fcdaa71b503535aa2b3c257740f3ecf055373
Merged-In: Ib04d80954bd8536914d88c66b28e6632e60a6245
diff --git a/services/tests/servicestests/src/com/android/server/wm/TaskStackContainersTests.java b/services/tests/servicestests/src/com/android/server/wm/TaskStackContainersTests.java
index ca1994f..9fa5ba4 100644
--- a/services/tests/servicestests/src/com/android/server/wm/TaskStackContainersTests.java
+++ b/services/tests/servicestests/src/com/android/server/wm/TaskStackContainersTests.java
@@ -18,20 +18,20 @@
 
 import static android.app.WindowConfiguration.ACTIVITY_TYPE_STANDARD;
 import static android.app.WindowConfiguration.WINDOWING_MODE_PINNED;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
+import android.platform.test.annotations.Presubmit;
+
+import androidx.test.filters.SmallTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.After;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
-import org.junit.Before;
-import org.junit.After;
-
-import android.platform.test.annotations.Presubmit;
-import android.support.test.filters.SmallTest;
-import android.support.test.runner.AndroidJUnit4;
 
 /**
  * Tests for the {@link DisplayContent.TaskStackContainers} container in {@link DisplayContent}.