input: Write a function to convert a given string to a different case. The function should use the string.swapcase() method to convert the case of each character in the string and return the modified string.
  
  def convert_string_case(string):
      new_string = string.swapcase()
      return new_string
  
  assert convert_string_case("this Is A TeST")=="THIS iS a tEst"
  assert convert_string_case("HelLo WoRlD")=="hELlO wOrLd"
  assert convert_string_case("12345")=="12345"
  assert convert_string_case("")==""
  assert convert_string_case("ABC")=="abc"
output: def convert_string_case(string):
      new_string = string.swapcase()
      return new_string