shadows/framework/src/main/java/org/robolectric/shadows/ShadowNotificationManager.java
@Implementation(minSdk = Build.VERSION_CODES.O)
  protected void deleteNotificationChannelGroup(String channelGroupId) {
    if (getNotificationChannelGroup(channelGroupId) != null) {
      // Deleting a channel group also deleted all associated channels. See
      // https://developer.android.com/reference/android/app/NotificationManager.html#deleteNotificationChannelGroup%28java.lang.String%29
      // for more info.
      for (/* NotificationChannel */ Object channel : getNotificationChannels()) {
        String groupId = ReflectionHelpers.callInstanceMethod(channel, "getGroup");
        if (channelGroupId.equals(groupId)) {
          String channelId = ReflectionHelpers.callInstanceMethod(channel, "getId");
          deleteNotificationChannel(channelId);
        }
      }
      notificationChannelGroups.remove(channelGroupId);
    }
  }
@Implementation(minSdk = Build.VERSION_CODES.O)
  protected void deleteNotificationChannelGroup(String channelGroupId) {
    if (getNotificationChannelGroup(channelGroupId) != null) {
      // Deleting a channel group also deleted all associated channels. See
      // https://developer.android.com/reference/android/app/NotificationManager.html#deleteNotificationChannelGroup%28java.lang.String%29
      // for more info.
      for (/* NotificationChannel */ Object channel : getNotificationChannels()) {
        String groupId = ReflectionHelpers.callInstanceMethod(channel, "getGroup");
        if (channelGroupId.equals(groupId)) {
          String channelId = ReflectionHelpers.callInstanceMethod(channel, "getId");
          deleteNotificationChannel(channelId);
        }
      }
      notificationChannelGroups.remove(channelGroupId);
    }
  }
Delete a notification channel group and all notification channels associated with the group.
This method will not notify any NotificationListenerService of resulting changes to
notification channel groups nor to notification channels.