if err != nil || prevNum > num {
			t.Errorf("got %v out of order, last was %v", obj, prevNum)
		}
		prevNum = num
	}
}

// Tests Heap.Add and ensures that heap invariant is preserved after adding items.
func TestHeap_Add(t *testing.T) {
	h := New(testHeapObjectKeyFunc, compareInts)
	h.Add(mkHeapObj("foo", 10))
	h.Add(mkHeapObj("bar", 1))
	h.Add(mkHeapObj("baz", 11))
	h.Add(mkHeapObj("zab", 30))