use strong_count and merge

Author: HoshimiP

tests/drop.rs

@@ -1,6 +1,7 @@
 use std::{
     sync::Arc,
     thread,
+    panic,
 };
 
 use ctor::ctor;
@@ -57,6 +58,31 @@ fn shared() {
     }
 
     assert_eq!(Arc::strong_count(&SHARED), 1);
+
+    let handles: Vec<_> = (0..9)
+        .map(|_| {
+            thread::spawn(move || {
+                let mut scope = Scope::new();
+                *SHARED.scope_mut(&mut scope) = SHARED.clone();
+                assert!(Arc::strong_count(&SHARED) >= 2);
+            })
+        })
+        .collect();
+
+    for h in handles {
+        h.join().unwrap();
+    }
+
+    assert_eq!(Arc::strong_count(&SHARED), 1);
+
+    let panic = panic::catch_unwind(|| {
+        let mut scope = Scope::new();
+        *SHARED.scope_mut(&mut scope) = SHARED.clone();
+        panic!("panic");
+    });
+    assert!(panic.is_err());
+
+    assert_eq!(Arc::strong_count(&SHARED), 1);
 }
 
 #[test]