input: Write a function to convert a given string to a different case using the swapcase() method. If the string is "this Is A TeST", the output should be "THIS iS a tEst".
  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("")==""
  assert convert_string_case("12345")=="12345"
  assert convert_string_case("Python3.8")=="pYTHON3.8"
output: def convert_string_case(string):
      new_string = string.swapcase()
      return new_string