Add test assertions that as_weak does not modify reference counts, and points to the right address.

Author: jeremyBanks

library/alloc/src/rc/tests.rs

@@ -103,6 +103,10 @@ fn test_weak_count() {
     let w = Rc::downgrade(&a);
     assert!(Rc::strong_count(&a) == 1);
     assert!(Rc::weak_count(&a) == 1);
+    let r = Rc::as_weak(&a);
+    assert!(Rc::strong_count(&a) == 1);
+    assert!(Rc::weak_count(&a) == 1);
+    assert!(r.as_ptr() == Rc::as_ptr(&a));
     drop(w);
     assert!(Rc::strong_count(&a) == 1);
     assert!(Rc::weak_count(&a) == 0);

library/alloc/src/sync/tests.rs

@@ -314,6 +314,10 @@ fn test_weak_count() {
     let w = Arc::downgrade(&a);
     assert!(Arc::strong_count(&a) == 1);
     assert!(Arc::weak_count(&a) == 1);
+    let r = Arc::as_weak(&a);
+    assert!(Arc::strong_count(&a) == 1);
+    assert!(Arc::weak_count(&a) == 1);
+    assert!(r.as_ptr() == Arc::as_ptr(&a));
     let x = w.clone();
     assert!(Arc::weak_count(&a) == 2);
     drop(w);