TopLevelStoragePreferenceControllerTest converted to JUnit

Helper function composed to return thread future, to guarantee
concurrent function finishes before test condition is checked.
Additionally a @VisibleForTesting helper function is used rather than
robolectric reflection helpers to set a class variable.

Fixes: 187249674
Test: atest -c TopLevelStoragePreferenceControllerTest
Change-Id: Ia22ebac4baec60f72b8516e9e79998cd788266ab
Merged-In: Ia22ebac4baec60f72b8516e9e79998cd788266ab
(cherry picked from commit 899eb7282d)

src/com/android/settings/deviceinfo/TopLevelStoragePreferenceController.java

@@ -21,6 +21,7 @@ import android.os.storage.StorageManager;
 import android.text.format.Formatter;
 import android.util.FeatureFlagUtils;
 
+import androidx.annotation.VisibleForTesting;
 import androidx.preference.Preference;
 
 import com.android.settings.R;
@@ -31,6 +32,7 @@ import com.android.settingslib.deviceinfo.StorageManagerVolumeProvider;
 import com.android.settingslib.utils.ThreadUtils;
 
 import java.text.NumberFormat;
+import java.util.concurrent.Future;
 
 public class TopLevelStoragePreferenceController extends BasePreferenceController {
 
@@ -59,10 +61,15 @@ public class TopLevelStoragePreferenceController extends BasePreferenceControlle
             return;
         }
 
-        ThreadUtils.postOnBackgroundThread(() -> {
+        refreshSummaryThread(preference);
+    }
+
+    @VisibleForTesting
+    protected Future refreshSummaryThread(Preference preference) {
+        return ThreadUtils.postOnBackgroundThread(() -> {
             final NumberFormat percentageFormat = NumberFormat.getPercentInstance();
             final PrivateStorageInfo info = PrivateStorageInfo.getPrivateStorageInfo(
-                    mStorageManagerVolumeProvider);
+                    getStorageManagerVolumeProvider());
             final double privateUsedBytes = info.totalBytes - info.freeBytes;
 
             ThreadUtils.postOnMainThread(() -> {
@@ -72,4 +79,10 @@ public class TopLevelStoragePreferenceController extends BasePreferenceControlle
             });
         });
     }
+
+
+    @VisibleForTesting
+    protected StorageManagerVolumeProvider getStorageManagerVolumeProvider() {
+        return mStorageManagerVolumeProvider;
+    }
 }