Make `AllSubsystems` usage easier in tests (#1794)

* Make `AllSubsystems` usage easier in tests

This makes the usage of `AllSubsystems` easier in tests by introducing
new methods.

- `dummy` initializes `AllSubsystems` with all systems set to dummy
- `replace_*` to replace any subsystem

Besides that this pr adds a `ForwardSubsystem` that is also useful for
tests. This subsystem will forward all incoming messages to the given channel.

* Update node/overseer/src/lib.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

* Update node/subsystem/src/lib.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

* Update node/subsystem/src/lib.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

* Move ForwardSubsystem and add a test

* Break some lines

Co-authored-by: Andronik Ordian <write@reusable.software>

Cargo.lock

@@ -5060,6 +5060,7 @@ dependencies = [
  "polkadot-node-primitives",
  "polkadot-node-subsystem",
  "polkadot-node-subsystem-util",
+ "polkadot-overseer",
  "polkadot-primitives",
  "polkadot-statement-table",
  "sc-network",

node/overseer/examples/minimal-example.rs

@@ -30,10 +30,7 @@ use kv_log_macro as log;
 use polkadot_primitives::v1::{BlockData, PoV};
 use polkadot_overseer::{Overseer, AllSubsystems};
 
-use polkadot_subsystem::{
-	Subsystem, SubsystemContext, DummySubsystem,
-	SpawnedSubsystem, FromOverseer,
-};
+use polkadot_subsystem::{Subsystem, SubsystemContext, SpawnedSubsystem, FromOverseer};
 use polkadot_subsystem::messages::{
 	CandidateValidationMessage, CandidateBackingMessage, AllMessages,
 };
@@ -141,23 +138,9 @@ fn main() {
 			Delay::new(Duration::from_secs(1)).await;
 		});
 
-		let all_subsystems = AllSubsystems {
-			candidate_validation: Subsystem2,
-			candidate_backing: Subsystem1,
-			candidate_selection: DummySubsystem,
-			statement_distribution: DummySubsystem,
-			availability_distribution: DummySubsystem,
-			bitfield_signing: DummySubsystem,
-			bitfield_distribution: DummySubsystem,
-			provisioner: DummySubsystem,
-			pov_distribution: DummySubsystem,
-			runtime_api: DummySubsystem,
-			availability_store: DummySubsystem,
-			network_bridge: DummySubsystem,
-			chain_api: DummySubsystem,
-			collation_generation: DummySubsystem,
-			collator_protocol: DummySubsystem,
-		};
+		let all_subsystems = AllSubsystems::<()>::dummy()
+			.replace_candidate_validation(Subsystem2)
+			.replace_candidate_backing(Subsystem1);
 		let (overseer, _handler) = Overseer::new(
 			vec![],
 			all_subsystems,

node/subsystem-test-helpers/Cargo.toml

@@ -22,3 +22,6 @@ polkadot-statement-table = { path = "../../statement-table" }
 sc-network = { git = "https://github.com/paritytech/substrate", branch = "master" }
 smallvec = "1.4.1"
 sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }
+
+[dev-dependencies]
+polkadot-overseer = { path = "../overseer" }

node/subsystem-test-helpers/src/lib.rs

@@ -17,7 +17,10 @@
 //! Utilities for testing subsystems.
 
 use polkadot_node_subsystem::messages::AllMessages;
-use polkadot_node_subsystem::{FromOverseer, SubsystemContext, SubsystemError, SubsystemResult};
+use polkadot_node_subsystem::{
+	FromOverseer, SubsystemContext, SubsystemError, SubsystemResult, Subsystem,
+	SpawnedSubsystem, OverseerSignal,
+};
 use polkadot_node_subsystem_util::TimeoutExt;
 
 use futures::channel::mpsc;
@@ -283,3 +286,59 @@ pub fn subsystem_test_harness<M, OverseerFactory, Overseer, TestFactory, Test>(
 			.expect("test timed out instead of completing")
 	});
 }
+
+/// A forward subsystem that implements [`Subsystem`].
+///
+/// It forwards all communication from the overseer to the internal message
+/// channel.
+///
+/// This subsystem is useful for testing functionality that interacts with the overseer.
+pub struct ForwardSubsystem<Msg>(pub mpsc::Sender<Msg>);
+
+impl<C: SubsystemContext<Message = Msg>, Msg: Send + 'static> Subsystem<C> for ForwardSubsystem<Msg> {
+	fn start(mut self, mut ctx: C) -> SpawnedSubsystem {
+		let future = Box::pin(async move {
+			loop {
+				match ctx.recv().await {
+					Ok(FromOverseer::Signal(OverseerSignal::Conclude)) => return,
+					Ok(FromOverseer::Communication { msg }) => {
+						let _ = self.0.send(msg).await;
+					},
+					Err(_) => return,
+					_ => (),
+				}
+			}
+		});
+
+		SpawnedSubsystem {
+			name: "forward-subsystem",
+			future,
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use polkadot_overseer::{Overseer, AllSubsystems};
+	use futures::executor::block_on;
+	use polkadot_node_subsystem::messages::CandidateSelectionMessage;
+
+	#[test]
+	fn forward_subsystem_works() {
+		let spawner = sp_core::testing::TaskExecutor::new();
+		let (tx, rx) = mpsc::channel(2);
+		let all_subsystems = AllSubsystems::<()>::dummy().replace_candidate_selection(ForwardSubsystem(tx));
+		let (overseer, mut handler) = Overseer::new(
+			Vec::new(),
+			all_subsystems,
+			None,
+			spawner.clone(),
+		).unwrap();
+
+		spawner.spawn("overseer", overseer.run().then(|_| async { () }).boxed());
+
+		block_on(handler.send_msg(CandidateSelectionMessage::Invalid(Default::default(), Default::default()))).unwrap();
+		assert!(matches!(block_on(rx.into_future()).0.unwrap(), CandidateSelectionMessage::Invalid(_, _)));
+	}
+}

node/subsystem/src/lib.rs

@@ -223,7 +223,7 @@ impl<C: SubsystemContext> Subsystem<C> for DummySubsystem {
 		});
 
 		SpawnedSubsystem {
-			name: "DummySubsystem",
+			name: "dummy-subsystem",
 			future,
 		}
 	}