Add a test that explicitly checks for a bad RedPallas binding signature in batch verification

Along with the explicit test for bad SpendAuth's in the batch.

zebra-chain/src/primitives/redpallas/tests/batch.rs

@@ -58,7 +58,7 @@ fn alternating_batch_verify() {
 }
 
 #[test]
-fn bad_batch_verify() {
+fn bad_spendauth_in_batch_verify() {
     let mut rng = thread_rng();
     let bad_index = 4; // must be even
     let mut batch = batch::Verifier::new();
@@ -97,3 +97,45 @@ fn bad_batch_verify() {
         }
     }
 }
+
+#[test]
+fn bad_binding_in_batch_verify() {
+    let mut rng = thread_rng();
+    let bad_index = 3; // must be odd
+    let mut batch = batch::Verifier::new();
+    let mut items = Vec::new();
+    for i in 0..32 {
+        let item: batch::Item = match i % 2 {
+            0 => {
+                let sk = SigningKey::<SpendAuth>::new(&mut rng);
+                let vk = VerificationKey::from(&sk);
+                let msg = b"BatchVerifyTest";
+                let sig = sk.sign(&mut rng, &msg[..]);
+                (vk.into(), sig, msg).into()
+            }
+            1 => {
+                let sk = SigningKey::<Binding>::new(&mut rng);
+                let vk = VerificationKey::from(&sk);
+                let msg = b"BatchVerifyTest";
+
+                let sig = if i != bad_index {
+                    sk.sign(&mut rng, &msg[..])
+                } else {
+                    sk.sign(&mut rng, b"bad")
+                };
+                (vk.into(), sig, msg).into()
+            }
+            _ => unreachable!(),
+        };
+        items.push(item.clone());
+        batch.queue(item);
+    }
+    assert!(batch.verify(rng).is_err());
+    for (i, item) in items.drain(..).enumerate() {
+        if i != bad_index {
+            assert!(item.verify_single().is_ok());
+        } else {
+            assert!(item.verify_single().is_err());
+        }
+    }
+}