Coordinator Batch signing test

substrate/in-instructions/primitives/src/lib.rs

@@ -82,6 +82,7 @@ impl Zeroize for SignedBatch {
   }
 }
 
+// TODO: Make this an associated method?
 /// The message for the batch signature.
 pub fn batch_message(batch: &Batch) -> Vec<u8> {
   [b"InInstructions-batch".as_ref(), &batch.encode()].concat()