Add test suite and minor refinements to the utility subsystem (#1403)

* get conclude signal working properly; don't allocate a vector

* wip: add test suite / example / explanation for using utility subsystem

Unfortunately, the test fails right now for reasons which seem
very odd. Just have to keep poking at it.

* explicitly import everything

* fix subsystem-util test

The root problem here was two-fold:

- there was a circular dependency from subsystem -> test-helpers/subsystem ->
  subsystem
- cfg(test) doesn't propagate between crates

The solution: move the subsystem test helpers into a sub-module
within subsystem. Publicly export them from the previous location
so no other code breaks.

Doing this has an additional benefit: it ensures that no production
code can ever accidentally use the subsystem helpers, as they are compile-
gated on cfg(test).

* fully commit to moving test helpers into a subsystem module

* add some more tests

* get rid of log tests in favor of real error forwarding

It's not obvious whether we'll ever really want to chase down
these errors outside a testing context, but having the capability
won't hurt.

* fix issue which caused test to hang on osx

* only require that job errors are PartialEq when testing

also fix polkadot-node-core-backing tests

* get rid of any notion of partialeq

* rethink testing

Combine tests of starting and stopping job: leaving a test executor
with a job running was pretty clearly the cause of the sometimes-hang.

Also, add a timeout so tests _can't_ hang anymore; they just fail
after a while.

* rename fwd_errors -> forward_errors

* warn on error propagation failure

* fix unused import leftover from merge

* derive eq for subsystemerror

polkadot/node/network/pov-distribution/src/lib.rs

@@ -620,7 +620,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 		let mut descriptor = CandidateDescriptor::default();
 		descriptor.pov_hash = pov_hash;
 
@@ -700,7 +700,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 		let mut descriptor = CandidateDescriptor::default();
 		descriptor.pov_hash = pov_hash;
 
@@ -778,7 +778,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			handle_network_update(
@@ -850,7 +850,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			// Peer A answers our request before peer B.
@@ -938,7 +938,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			// Peer A answers our request: right relay parent, awaited hash, wrong PoV.
@@ -1001,7 +1001,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			// Peer A answers our request: right relay parent, awaited hash, wrong PoV.
@@ -1062,7 +1062,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			// Peer A answers our request: right relay parent, awaited hash, wrong PoV.
@@ -1120,7 +1120,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			let max_plausibly_awaited = n_validators * 2;
@@ -1205,7 +1205,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			let pov_hash = make_pov(vec![1, 2, 3]).hash();
@@ -1267,7 +1267,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			let pov_hash = make_pov(vec![1, 2, 3]).hash();
@@ -1344,7 +1344,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			handle_network_update(
@@ -1427,7 +1427,7 @@ mod tests {
 		};
 
 		let pool = sp_core::testing::SpawnBlockingExecutor::new();
-		let (mut ctx, mut handle) = subsystem_test::make_subsystem_context(pool);
+		let (mut ctx, mut handle) = polkadot_subsystem::test_helpers::make_subsystem_context(pool);
 
 		executor::block_on(async move {
 			handle_network_update(