Remove transaction-pool test-helpers feature (#10571)

* Remove transaction-pool `test-helpers` feature

`test-helpers` feature is a bad idea in general, because once the feature is enabled somewhere in
the workspace, it is enabled anywhere. While removing the feature, the tests were also rewritten to
get rid off other "only test" related code.

Contributes towards: https://github.com/paritytech/substrate/issues/9727

* Apply suggestions from code review

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Fix benches

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

substrate/client/transaction-pool/src/lib.rs

@@ -23,20 +23,12 @@
 #![warn(unused_extern_crates)]
 
 mod api;
+pub mod error;
 mod graph;
 mod metrics;
 mod revalidation;
-
-pub mod error;
-
-/// Common types for testing the transaction pool
-#[cfg(feature = "test-helpers")]
-pub mod test_helpers {
-	pub use super::{
-		graph::{BlockHash, ChainApi, ExtrinsicFor, NumberFor, Pool},
-		revalidation::RevalidationQueue,
-	};
-}
+#[cfg(test)]
+mod tests;
 
 pub use crate::api::FullChainApi;
 use futures::{
@@ -170,13 +162,10 @@ where
 	PoolApi: graph::ChainApi<Block = Block> + 'static,
 {
 	/// Create new basic transaction pool with provided api, for tests.
-	#[cfg(feature = "test-helpers")]
-	pub fn new_test(
-		pool_api: Arc<PoolApi>,
-	) -> (Self, Pin<Box<dyn Future<Output = ()> + Send>>, intervalier::BackSignalControl) {
+	pub fn new_test(pool_api: Arc<PoolApi>) -> (Self, Pin<Box<dyn Future<Output = ()> + Send>>) {
 		let pool = Arc::new(graph::Pool::new(Default::default(), true.into(), pool_api.clone()));
-		let (revalidation_queue, background_task, notifier) =
-			revalidation::RevalidationQueue::new_test(pool_api.clone(), pool.clone());
+		let (revalidation_queue, background_task) =
+			revalidation::RevalidationQueue::new_background(pool_api.clone(), pool.clone());
 		(
 			Self {
 				api: pool_api,
@@ -187,7 +176,6 @@ where
 				metrics: Default::default(),
 			},
 			background_task,
-			notifier,
 		)
 	}
 
@@ -237,7 +225,6 @@ where
 	}
 
 	/// Get access to the underlying api
-	#[cfg(feature = "test-helpers")]
 	pub fn api(&self) -> &PoolApi {
 		&self.api
 	}