Convert other exercises that have assertions to test mode

exercises/iterators/iterators1.rs

@@ -11,6 +11,7 @@
 
 // I AM NOT DONE
 
+#[test]
 fn main() {
     let my_fav_fruits = vec!["banana", "custard apple", "avocado", "peach", "raspberry"];
 

exercises/smart_pointers/rc1.rs

@@ -35,6 +35,7 @@ impl Planet {
     }
 }
 
+#[test]
 fn main() {
     let sun = Rc::new(Sun {});
     println!("reference count = {}", Rc::strong_count(&sun)); // 1 reference

exercises/threads/threads3.rs

@@ -48,6 +48,7 @@ fn send_tx(q: Queue, tx: mpsc::Sender<u32>) -> () {
     });
 }
 
+#[test]
 fn main() {
     let (tx, rx) = mpsc::channel();
     let queue = Queue::new();