Add basic submitpackage test

We don't actually test package submission semantics, but most of the
type de/ser logic by submitting a package of two already-known txs.

integration_test/src/v28/raw_transactions.rs

@@ -6,11 +6,70 @@
 //! API docs of `bitcoind v28.0`.
 
 /// Requires `Client` to be in scope
-#[macro_export] macro_rules! impl_test_v28__submitpackage {
+#[macro_export]
+macro_rules! impl_test_v28__submitpackage {
     () => {
         #[test]
         fn submitpackage() {
-            // TODO
+            //let bitcoind = $crate::bitcoind_no_wallet();
+
+            let bitcoind = $crate::bitcoind_with_default_wallet();
+
+            // Submitting the empty package should simply fail.
+            assert!(bitcoind.client.submit_package(&[], None, None).is_err());
+
+            // Premine to get some funds
+            let address = bitcoind.client.new_address().expect("failed to get new address");
+            let json =
+                bitcoind.client.generate_to_address(101, &address).expect("generatetoaddress");
+            json.into_model().unwrap();
+
+            // Send to ourselves, mine, send again to generate two transactions.
+            let (tx_0, tx_1) = {
+                let new_address = bitcoind.client.new_address().expect("failed to get new address");
+                let txid = bitcoind
+                    .client
+                    .send_to_address(&new_address, bitcoin::Amount::from_sat(1000000))
+                    .unwrap()
+                    .into_model()
+                    .unwrap()
+                    .txid;
+
+                let _ =
+                    bitcoind.client.generate_to_address(1, &address).expect("generatetoaddress");
+
+                let best_block_hash = bitcoind.client.best_block_hash().unwrap();
+                let best_block = bitcoind.client.get_block(best_block_hash).unwrap();
+                let tx_0 = best_block.txdata[1].clone();
+
+                let new_address = bitcoind.client.new_address().expect("failed to get new address");
+                let txid = bitcoind
+                    .client
+                    .send_to_address(&new_address, bitcoin::Amount::from_sat(1000000))
+                    .unwrap()
+                    .into_model()
+                    .unwrap()
+                    .txid;
+
+                let _ =
+                    bitcoind.client.generate_to_address(1, &address).expect("generatetoaddress");
+
+                let best_block_hash = bitcoind.client.best_block_hash().unwrap();
+                let best_block = bitcoind.client.get_block(best_block_hash).unwrap();
+                let tx_1 = best_block.txdata[1].clone();
+                (tx_0, tx_1)
+            };
+
+            // The call for submitting this package should succeed, but yield an 'already known'
+            // error for all transactions.
+            let res = bitcoind
+                .client
+                .submit_package(&[tx_0, tx_1], None, None)
+                .expect("failed to submit package");
+            for (_, tx_result) in &res.tx_results {
+                assert!(tx_result.error.is_some());
+            }
+            assert!(res.replaced_transactions.is_empty());
         }
     };
 }