From b1cdb4f3fbd90e76baa743ecb8d60b13249498bd Mon Sep 17 00:00:00 2001
From: timofey <tim@ongoteam.yaconnect.com>
Date: Sun, 15 Oct 2023 12:52:49 +0000
Subject: [PATCH] `cannot_refer_to_empty`

---
 src/rstd/collections/tree.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/rstd/collections/tree.rs b/src/rstd/collections/tree.rs
index ad18226..5c18e48 100644
--- a/src/rstd/collections/tree.rs
+++ b/src/rstd/collections/tree.rs
@@ -265,6 +265,13 @@ mod tests {
         assert_eq!(trees.height(&trees.empty()), 0);
     }
 
+    #[test]
+    fn cannot_refer_to_empty() {
+        let trees = BalancedTrees::new(new_trees());
+        let tree = trees.empty();
+        assert!(trees.refer(&tree).is_none());
+    }
+
     #[test]
     fn one_has_height_1() {
         let trees = BalancedTrees::new(new_trees());