From fe967279e5055f0786b44f13c8efc82bd0794f32 Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Tue, 24 Sep 2024 12:40:30 +1000
Subject: [PATCH] Improve witness unit tests for single empty element

The current unit test is incorrect, the indices field of a witness with
a single element starts at 1 because 0 is encode as a single
byte (compact encoded integer).

Fix the debug test and add a test that pushes an empty slice.
---
 bitcoin/src/blockdata/witness.rs | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/bitcoin/src/blockdata/witness.rs b/bitcoin/src/blockdata/witness.rs
index 432079e68..74e3e4540 100644
--- a/bitcoin/src/blockdata/witness.rs
+++ b/bitcoin/src/blockdata/witness.rs
@@ -645,16 +645,33 @@ mod test {
         v
     }
 
-    #[test]
-    fn witness_debug_can_display_empty_instruction() {
-        let witness = Witness {
+    // A witness with a single element that is empty (zero length).
+    fn single_empty_element() -> Witness {
+        // The first is 0 serialized as a compact size integer.
+        // The last four bytes represent start at index 0.
+        let content = [0_u8; 5];
+
+        Witness {
             witness_elements: 1,
-            content: append_u32_vec(vec![], &[0]),
-            indices_start: 2,
-        };
+            content: content.to_vec(),
+            indices_start: 1,
+        }
+    }
+
+    #[test]
+    fn witness_debug_can_display_empty_element() {
+        let witness = single_empty_element();
         println!("{:?}", witness);
     }
 
+    #[test]
+    fn witness_single_empty_element() {
+        let mut got = Witness::new();
+        got.push(&[]);
+        let want = single_empty_element();
+        assert_eq!(got, want)
+    }
+
     #[test]
     fn test_push() {
         let mut witness = Witness::default();