code: def test_set_logger_formatter_existing_handler():
      """Shared - Set Logger Formatter, Existing Handler"""
      logger = logging.getLogger("test")  # non-root logger
  
      # Create handler to be added
      # This simulates what happens in the Lambda execution environment
      handler = logging.StreamHandler()
      logger.addHandler(handler)
  
      # Now set the formatter on the logger that already has a handler
      set_formatter(logger)
  
      assert_is_instance(handler.formatter, LogFormatter)
  
file_path: streamalert/tests/unit/streamalert/shared/test_logger.py
imports: import logging
  import os
  from mock import patch
  from nose.tools import assert_equal, assert_is_instance
  from streamalert.shared.logger import get_logger, LogFormatter, set_formatter
label_desc: Use image node_id 5 for calling a global function with example usage: test_set_logger_formatter_existing_handler() without return types