Add test for re-heapify using boxed closure.

Author: sekineh

src/liballoc/tests/binary_heap.rs

@@ -259,12 +259,26 @@ fn test_from_iter() {
 
 #[test]
 fn test_from_vec_cmp() {
-    let vec = vec![9, 8, 7, 6, 5, 4, 3, 2, 1];
-    let cmp = |a: &i32, b: &i32| b.partial_cmp(a);
+    // closure
+    let heap = BinaryHeap::from((vec![2, 3, 89, 5, 8, 1, 13, 21, 34, 55, 1],
+                                 |a: &i32, b: &i32| b.partial_cmp(a)));
+    assert_eq!(heap.into_iter_sorted().collect::<Vec<_>>(),
+               vec![1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]);
+}
 
-    let heap = BinaryHeap::from((vec, cmp));
-    assert_eq!(heap.into_iter_sorted().collect::<Vec<_>>(), 
-        vec![1, 2, 3, 4, 5, 6, 7, 8, 9]);
+#[test]
+fn test_from_vec_cmp_boxed_closure() {
+    // boxed closure
+    let vec = vec![2, 3, 89, 5, 8, 1, 13, 21, 34, 55, 1];
+    let cmp1: Box<dyn Fn(&i32, &i32) -> Option<core::cmp::Ordering>> = Box::new(|a: &i32, b: &i32| a.partial_cmp(b));
+    let cmp2: Box<dyn Fn(&i32, &i32) -> Option<core::cmp::Ordering>> = Box::new(|a: &i32, b: &i32| b.partial_cmp(a));
+
+    let mut heap = BinaryHeap::from((vec, cmp1));
+    assert_eq!(heap.pop(), Some(89));
+
+    // re-heapify using different comparator
+    heap = BinaryHeap::from((heap.into(), cmp2));
+    assert_eq!(heap.pop(), Some(1));
 }
 
 #[test]