input: Write a function to convert a given string to a different case using the swapcase() method. The function should return the new 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("Python3")=="pYTHON3"
  assert convert_string_case("")==""
output: def convert_string_case(string):
      new_string = string.swapcase()
      return new_string