code: def test_handler(mock_instance):
      """Alert Merger - Handler (Entry Point)"""
      main.handler(None, None)
      mock_instance.assert_has_calls(
          [call.get_instance(), call.get_instance().dispatch()]
      )
  
imports: from datetime import datetime, timedelta
  import os
  from mock import ANY, call, patch, MagicMock
  from moto import mock_dynamodb2, mock_lambda
  from nose.tools import assert_equal, assert_false, assert_true
  from streamalert.alert_merger import main
  from streamalert.shared.alert import Alert
  from tests.unit.helpers.aws_mocks import create_lambda_function, setup_mock_alerts_table
label_desc: Use image node_id 1 for calling a global function with example usage: test_handler(mock_instance) without return types