add proxy_alloc_observe_test

zeroize/tests/alloc.rs

@@ -48,3 +48,26 @@ fn proxy_alloc_test() {
     let b2 = SecretBox::new([u8::MAX; 160]);
     core::hint::black_box(&b2);
 }
+
+struct ObserveSecretBox<S: Zeroize + Default>(Box<S>);
+
+impl<S: Zeroize + Default> ObserveSecretBox<S> {
+    fn new(val: S) -> Self {
+        Self(Box::new(val))
+    }
+}
+
+impl<S: Zeroize + Default> Drop for ObserveSecretBox<S> {
+    fn drop(&mut self) {
+        *self.0 = S::default();
+        zeroize::observe(self);
+    }
+}
+
+#[test]
+fn proxy_alloc_observe_test() {
+    let b1 = ObserveSecretBox::new([u128::MAX; 10]);
+    core::hint::black_box(&b1);
+    let b2 = ObserveSecretBox::new([u64::MAX; 20]);
+    core::hint::black_box(&b2);
+}