add test_pop_last

mempool/src/lib.rs

@@ -106,6 +106,17 @@ mod tests {
         assert_eq!(pool.len(), 1);
     }
 
+    #[test]
+    fn test_pop_last() {
+        let mut pool = MemPool::new();
+        pool.push_item(test_item_with_id(1));
+        pool.push_item(test_item_with_id(2));
+        let item = pool.pop_last();
+        assert_eq!(item, Some(test_item_with_id(1)));
+        assert_eq!(pool.len(), 1);
+    }
+
+
     #[test]
     fn test_push_pop() {
         let mut mempool: MemPool<TestItem> = MemPool::new();