### Question:
ButtonApiImpl implements ButtonApi { @Override public void setApplicationId(String applicationId) { connectionManager.setApplicationId(applicationId); } @VisibleForTesting  ButtonApiImpl(ConnectionManager connectionManager); @Override void setApplicationId(String applicationId); @Nullable @Override String getApplicationId(); @Nullable @WorkerThread @Override PostInstallLink getPendingLink(String applicationId, @Nullable String advertisingId,
            Map<String, String> signalsMap); @Nullable @Override Void postOrder(Order order, String applicationId, String sourceToken,
            @Nullable String advertisingId); @Nullable @Override Void postActivity(String activityName, List<ButtonProductCompatible> products,
            @Nullable String sourceToken, @Nullable String advertisingId); @Nullable @Override Void postEvents(List<Event> events, @Nullable String advertisingId);  }### Answer:
@Test public void setApplicationId_shouldProvideToConnectionManager() { buttonApi.setApplicationId("valid_application_id"); verify(connectionManager).setApplicationId("valid_application_id"); }