Test more of Vec::peek_mut

Author: cammeresi

library/alloctests/tests/vec.rs

@@ -2643,15 +2643,16 @@ fn test_peek_mut() {
     assert!(vec.peek_mut().is_none());
     vec.push(1);
     vec.push(2);
-    if let Some(mut p) = vec.peek_mut() {
-        assert_eq!(*p, 2);
-        *p = 0;
-        assert_eq!(*p, 0);
-        PeekMut::pop(p);
-        assert_eq!(vec.len(), 1);
-    } else {
-        unreachable!()
-    }
+    let mut p = vec.peek_mut().unwrap();
+    assert_eq!(*p, 2);
+    *p = 0;
+    assert_eq!(*p, 0);
+    drop(p);
+    assert_eq!(vec, vec![1, 0]);
+    let p = vec.peek_mut().unwrap();
+    let p = PeekMut::pop(p);
+    assert_eq!(p, 0);
+    assert_eq!(vec, vec![1]);
 }
 
 /// This assortment of tests, in combination with miri, verifies we handle UB on fishy arguments