[Audiosharing] Add tests.

Test: atest -c com.android.settings.connecteddevice.audiosharing.audiostreams
Bug: 308368124
Change-Id: I6322ccbb5deffe2bc169a898ef0208e135caa819

src/com/android/settings/connecteddevice/audiosharing/audiostreams/AudioStreamsHelper.java

@@ -139,8 +139,10 @@ public class AudioStreamsHelper {
                 .toList();
     }
 
+    /** Retrieves LocalBluetoothLeBroadcastAssistant. */
+    @VisibleForTesting
     @Nullable
-    LocalBluetoothLeBroadcastAssistant getLeBroadcastAssistant() {
+    public LocalBluetoothLeBroadcastAssistant getLeBroadcastAssistant() {
         return mLeBroadcastAssistant;
     }