code: def test_get_channel_with_multi_recipients() -> None:
      """
      Test the _get_channel function to ensure it will return a string
      with recipients separated by commas without interstitial spacing
      """
      from superset.reports.models import (
          ReportRecipients,
          ReportRecipientType,
      )
      from superset.reports.notifications.base import (
          NotificationContent,
      )
      from superset.reports.notifications.slack import SlackNotification
  
      content = NotificationContent(
          name="test alert",
          header_data={
              "notification_format": "PNG",
              "notification_type": "Alert",
              "owners": [1],
              "notification_source": None,
              "chart_id": None,
              "dashboard_id": None,
          },
          embedded_data=pd.DataFrame(
              {
                  "A": [1, 2, 3],
                  "B": [4, 5, 6],
                  "C": [
                      "111",
                      "222",
                      '<a href="http://www.example.com">333</a>',
                  ],
              }
          ),
          description='<p>This is <a href="#">a test</a> alert</p><br />',
      )
      slack_notification = SlackNotification(
          recipient=ReportRecipients(
              type=ReportRecipientType.SLACK,
              recipient_config_json='{"target": "some_channel; second_channel, third_channel"}',
          ),
          content=content,
      )
  
      result = slack_notification._get_channel()
  
      assert result == "some_channel,second_channel,third_channel"
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_get_channel_with_multi_recipients() without return types