Add failure test cases for max_mpp_path_count.

Author: tnull

lightning/src/routing/router.rs

@@ -4111,6 +4111,26 @@ mod tests {
 			} else { panic!(); }
 		}
 
+		{
+			// Attempt to route while setting max_mpp_path_count to 0 results in a failure..
+			let zero_payment_params = payment_params.clone().with_max_mpp_path_count(0);
+			if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(
+					&our_id, &zero_payment_params, &network_graph.read_only(), None, 100, 42, Arc::clone(&logger), &scorer, &random_seed_bytes) {
+				assert_eq!(err, "Can't find an MPP route with no paths allowed.");
+			} else { panic!(); }
+		}
+
+		{
+			// Attempt to route while setting max_mpp_path_count to 3 results in a failure..
+			// This is the case because the minimal_value_contribution_msat would require each path
+			// to account for 1/3 of the total value, which is violated by 2 out of 3 paths.
+			let fail_payment_params = payment_params.clone().with_max_mpp_path_count(3);
+			if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(
+					&our_id, &fail_payment_params, &network_graph.read_only(), None, 250_000, 42, Arc::clone(&logger), &scorer, &random_seed_bytes) {
+				assert_eq!(err, "Failed to find a sufficient route to the given destination");
+			} else { panic!(); }
+		}
+
 		{
 			// Now, attempt to route 250 sats (just a bit below the capacity).
 			// Our algorithm should provide us with these 3 paths.