Make generated block proposals cancel each other out

linera-client/src/client_context.rs

@@ -877,7 +877,11 @@ where
         fungible_application_id: Option<ApplicationId>,
     ) -> Vec<RpcMessage> {
         let mut proposals = Vec::new();
-        let mut next_recipient = self.wallet.last_chain().unwrap().chain_id;
+        let mut next_recipient = *key_pairs
+            .iter()
+            .last()
+            .expect("There should be a last element")
+            .0;
         let amount = Amount::from(1);
         for (&chain_id, key_pair) in key_pairs {
             let public_key = key_pair.public();

linera-service/src/linera/main.rs

@@ -747,6 +747,11 @@ impl Runnable for Job {
                 transactions_per_block,
                 fungible_application_id,
             } => {
+                assert!(num_chains > 0, "Number of chains must be greater than 0");
+                assert!(
+                    transactions_per_block > 0,
+                    "Number of transactions per block must be greater than 0"
+                );
                 let start = Instant::now();
                 // Below all block proposals are supposed to succeed without retries, we
                 // must make sure that all incoming payments have been accepted on-chain