input: Write a function to convert a given string to a different case. The function should swap the case of each character in the string. If the string contains any non-alphabetic characters, they should remain unchanged.
  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("Python3.8")=="pYTHON3.8"
output: def convert_string_case(string):
      new_string = string.swapcase()
      return new_string