input: Write a python function to parse a JSON string and extract employee names.
  assert extract_employee_names('{"employees":[ {"id":1,"firstName":"John","lastName":"Doe"}, {"id":2,"firstName":"Jane","lastName":"Doe"} ]}') == [('John', 'Doe'), ('Jane', 'Doe')]
  assert extract_employee_names('{"employees":[ {"id":1,"firstName":"Alice","lastName":"Smith"}, {"id":2,"firstName":"Bob","lastName":"Brown"} ]}') == [('Alice', 'Smith'), ('Bob', 'Brown')]
  assert extract_employee_names('{"employees":[ {"id":1,"firstName":"Charlie","lastName":"Johnson"}, {"id":2,"firstName":"Dana","lastName":"White"} ]}') == [('Charlie', 'Johnson'), ('Dana', 'White')]
output: import json
  
  def extract_employee_names(json_string):
      data = json.loads(json_string)
      employees = data['employees']
      return [(employee['firstName'], employee['lastName']) for employee in employees]