content: class DummyFile:
      write_count: int = 0
      write_gen_count: int = 0
  
      def write(self, s: str):
          self.write_count += 1
      def __file_write_gen__(self, g):
          self.write_gen_count += 1
  
  @test
  def test_file_io():
      f = DummyFile()
      f.write('')                                     # opt not applied
      f.write('hello world')                          # opt not applied
      f.write(str.cat("hello ", "world"))             # opt applied
      a, b, c = 3.14, 'xyz', 42
      f.write(f'hello {a} world {b=} abc {a+c} zzz')  # opt applied
      f.write(f'hello world')                         # opt applied
      assert f.write_count == 2
      assert f.write_gen_count == 3
  test_file_io()
  
  @test
  def test_print():
      from sys import stdout
      print('hello world')               # EXPECT: hello world
      print(str.cat("hello ", "world"))  # EXPECT: hello world
      a, b, c = 3.14, 'xyz', 42
      print(f'hello {a} world {b=} abc {a+c} zzz', file=stdout, sep='x')  # EXPECT: hello 3.14 world b=xyz abc 45.14 zzz
      print(f'hello', f'world', sep='x')  # EXPECT: helloxworld
  test_print()
  