Iterator: Test that Iterator can be used in a for loop

`for x in foo` depends on foo implementing IntoIterator.

gstreamer/src/iterator.rs

@@ -767,6 +767,15 @@ mod tests {
         assert_eq!(it.next(), None);
     }
 
+    #[test]
+    fn test_into_iter() {
+        let mut v = vec![1i32, 2, 3].into_iter();
+        for x in Iterator::from_vec(vec![1i32, 2, 3]) {
+            assert_eq!(x.unwrap(), v.next().unwrap());
+        }
+        assert_eq!(v.next(), None);
+    }
+
     #[test]
     fn test_std_resync_collect() {
         use prelude::*;