input: Write a function to convert a given string to a different case, specifically by swapping the case of each character.
  assert convert_string_case("this Is A TeST")=="THIS iS a tEst"
  assert convert_string_case("HeLlO wOrLd")=="hElLo WoRlD"
  assert convert_string_case("ALLCAPS")=="allcaps"
  assert convert_string_case("nocaps")=="NOCAPS"
  assert convert_string_case("")==""
output: def convert_string_case(s):
      return s.swapcase()