Make all tests not output anything

tests/advanced1.rs

@@ -11,7 +11,7 @@ fn steps(machine: &mut rustijvm::Machine, num: usize) {
 
 #[test]
 fn advanced1() {
-    let output: Arc<Mutex<Cursor<Vec<u8>>>> = Arc::new(Mutex::new(Cursor::new(Vec::new())));
+    let output = rustijvm::stubs::output_stub();
     let input = Box::new("A".as_bytes());
     let mut machine = rustijvm::Machine::new_from_file("files/task5/all_regular.ijvm").unwrap();
     machine.set_input(input);