f significantly improve readability of test_path_paused_mpp thanks to

Jeff

Author: TheBlueMatt

lightning/src/ln/chanmon_update_fail_tests.rs

@@ -1765,7 +1765,7 @@ fn during_funding_monitor_fail() {
 
 #[test]
 fn test_path_paused_mpp() {
-	// Simple test of sending a multi-path payment where one path is currently blocked awaiting
+	// Simple test of sending a multi-part payment where one path is currently blocked awaiting
 	// monitor update
 	let chanmon_cfgs = create_chanmon_cfgs(4);
 	let node_cfgs = create_node_cfgs(4, &chanmon_cfgs);
@@ -1780,6 +1780,8 @@ fn test_path_paused_mpp() {
 	let (payment_preimage, payment_hash) = get_payment_preimage_hash!(&nodes[0]);
 	let payment_secret = PaymentSecret([0xdb; 32]);
 	let mut route = nodes[0].router.get_route(&nodes[3].node.get_our_node_id(), None, &[], 100000, TEST_FINAL_CLTV).unwrap();
+
+	// Set us up to take multiple routes, one 0 -> 1 -> 3 and one 0 -> 2 -> 3:
 	let path = route.paths[0].clone();
 	route.paths.push(path);
 	route.paths[0][0].pubkey = nodes[1].node.get_our_node_id();
@@ -1789,21 +1791,29 @@ fn test_path_paused_mpp() {
 	route.paths[1][0].short_channel_id = chan_2_ann.contents.short_channel_id;
 	route.paths[1][1].short_channel_id = chan_4_id;
 
+	// Set it so that the first monitor update (for the path 0 -> 1 -> 3) succeeds, but the second
+	// (for the path 0 -> 2 -> 3) fails.
 	*nodes[0].chan_monitor.update_ret.lock().unwrap() = Ok(());
 	*nodes[0].chan_monitor.next_update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::TemporaryFailure));
 
-	if let Err(PaymentSendFailure::PartialFailure(fails)) = nodes[0].node.send_payment(&route, payment_hash, &Some(payment_secret)) {
-		assert_eq!(fails.len(), 2);
-		if let Ok(()) = fails[0] {} else { panic!(); }
-		if let Err(APIError::MonitorUpdateFailed) = fails[1] {} else { panic!(); }
+	// Now check that we get the right return value, indicating that the first path succeeded but
+	// the second got a MonitorUpdateFailed err. This implies PaymentSendFailure::PartialFailure as
+	// some paths succeeded, preventing retry.
+	if let Err(PaymentSendFailure::PartialFailure(results)) = nodes[0].node.send_payment(&route, payment_hash, &Some(payment_secret)) {
+		assert_eq!(results.len(), 2);
+		if let Ok(()) = results[0] {} else { panic!(); }
+		if let Err(APIError::MonitorUpdateFailed) = results[1] {} else { panic!(); }
 	} else { panic!(); }
 	check_added_monitors!(nodes[0], 2);
 	*nodes[0].chan_monitor.update_ret.lock().unwrap() = Ok(());
 
+	// Pass the first HTLC of the payment along to nodes[3].
 	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
 	assert_eq!(events.len(), 1);
 	pass_along_path(&nodes[0], &[&nodes[1], &nodes[3]], 0, payment_hash.clone(), Some(payment_secret), events.pop().unwrap(), false);
 
+	// And check that, after we successfully update the monitor for chan_2 we can pass the second
+	// HTLC along to nodes[3] and claim the whole payment back to nodes[0].
 	let (outpoint, latest_update) = nodes[0].chan_monitor.latest_monitor_update_id.lock().unwrap().get(&chan_2_id).unwrap().clone();
 	nodes[0].node.channel_monitor_updated(&outpoint, latest_update);
 	let mut events = nodes[0].node.get_and_clear_pending_msg_events();