From 9e618bacf2c060d19d7dfbdb04c332b81cf56839 Mon Sep 17 00:00:00 2001
From: Stein Somers <git@steinsomers.be>
Date: Wed, 18 Nov 2020 18:19:38 +0100
Subject: [PATCH] BTreeMap: make test cases more explicit on failure

---
 library/alloc/src/collections/btree/map/tests.rs  |  2 +-
 library/alloc/src/collections/btree/node/tests.rs | 12 ++++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/library/alloc/src/collections/btree/map/tests.rs b/library/alloc/src/collections/btree/map/tests.rs
index 97df8ea07d23e..c857d4317e495 100644
--- a/library/alloc/src/collections/btree/map/tests.rs
+++ b/library/alloc/src/collections/btree/map/tests.rs
@@ -115,7 +115,7 @@ impl<K, V> BTreeMap<K, V> {
 
 impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal> {
     fn assert_min_len(self, min_len: usize) {
-        assert!(self.len() >= min_len, "{} < {}", self.len(), min_len);
+        assert!(self.len() >= min_len, "node len {} < {}", self.len(), min_len);
         if let node::ForceResult::Internal(node) = self.force() {
             for idx in 0..=node.len() {
                 let edge = unsafe { Handle::new_edge(node, idx) };
diff --git a/library/alloc/src/collections/btree/node/tests.rs b/library/alloc/src/collections/btree/node/tests.rs
index 6886962106b02..7fe8ff743c040 100644
--- a/library/alloc/src/collections/btree/node/tests.rs
+++ b/library/alloc/src/collections/btree/node/tests.rs
@@ -30,11 +30,15 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
                 let depth = self.height();
                 let indent = "  ".repeat(depth);
                 result += &format!("\n{}", indent);
-                for idx in 0..leaf.len() {
-                    if idx > 0 {
-                        result += ", ";
+                if leaf.len() == 0 {
+                    result += "(empty node)";
+                } else {
+                    for idx in 0..leaf.len() {
+                        if idx > 0 {
+                            result += ", ";
+                        }
+                        result += &format!("{:?}", unsafe { leaf.key_at(idx) });
                     }
-                    result += &format!("{:?}", unsafe { leaf.key_at(idx) });
                 }
             }
             navigate::Position::Internal(_) => {}