input: Write a function to convert a given string to a different case using the swapcase() method. Return the new string with the swapped case.
  
  def convert_string_case(string):
      return string.swapcase()
  
  assert convert_string_case("this Is A TeST")=="THIS iS a tEst"
  assert convert_string_case("HELLO World")=="hello wORLD"
  assert convert_string_case("onlyLOWERCASE")=="ONLYupperCASE"
  assert convert_string_case("ALLUPPERCASE")=="alluppercase"
  assert convert_string_case("")==""
output: def convert_string_case(string):
      return string.swapcase()