Make all tests not output anything

tests/advanced4.rs

@@ -5,8 +5,9 @@ use std::io::{Cursor, Seek, SeekFrom, Read};
 
 #[test]
 fn advanced4_tanenbaum() {
-    let rc = Arc::new(Mutex::new(Cursor::new(Vec::new())));
+    let rc = rustijvm::stubs::output_stub();
     let mut machine = rustijvm::Machine::new_from_file("files/advanced/Tanenbaum.ijvm").unwrap();
+
     machine.set_output(rc.clone());
     machine.run().unwrap();