Use `TEST_WS` in all remote-externalities tests (#3284)

Refactor in accordance with
https://github.com/paritytech/polkadot-sdk/issues/2245#issuecomment-1937025951

Prior to this PR, the `remote_tests` test module would either use
`TEST_WS` or `DEFAULT_HTTP_ENDPOINT`.

With the PR, `TEST_WS` is the default for the `remote_tests` test module
and the fallback is `DEFAULT_HTTP_ENDPOINT`.

The only downside I see to this PR is that for particular tests in the
`remote_tests` module, one would want to use a different http endpoint.
If that is the case, they would have to manually hardcode the http
endpoint for that particular test.

Note: The `TEST_WS` node should fulfill the role for all test cases e.g.
include child tries.

Give it a _try_:
```
TEST_WS=wss://rococo-try-runtime-node.parity-chains.parity.io:443 cargo test --features=remote-test -p frame-remote-externalities -- --nocapture
```

---------

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/utils/frame/remote-externalities/src/lib.rs

@@ -1263,7 +1263,11 @@ mod tests {
 #[cfg(all(test, feature = "remote-test"))]
 mod remote_tests {
 	use super::test_prelude::*;
-	use std::os::unix::fs::MetadataExt;
+	use std::{env, os::unix::fs::MetadataExt};
+
+	fn endpoint() -> String {
+		env::var("TEST_WS").unwrap_or_else(|_| DEFAULT_HTTP_ENDPOINT.to_string())
+	}
 
 	#[tokio::test]
 	async fn state_version_is_kept_and_can_be_altered() {
@@ -1273,6 +1277,7 @@ mod remote_tests {
 		// first, build a snapshot.
 		let ext = Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				pallets: vec!["Proxy".to_owned()],
 				child_trie: false,
 				state_snapshot: Some(SnapshotConfig::new(CACHE)),
@@ -1314,6 +1319,7 @@ mod remote_tests {
 		// first, build a snapshot.
 		let ext = Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				pallets: vec!["Proxy".to_owned()],
 				child_trie: false,
 				state_snapshot: Some(SnapshotConfig::new(CACHE)),
@@ -1341,6 +1347,7 @@ mod remote_tests {
 		// create an ext with children keys
 		let child_ext = Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				pallets: vec!["Proxy".to_owned()],
 				child_trie: true,
 				state_snapshot: Some(SnapshotConfig::new(CACHE)),
@@ -1353,6 +1360,7 @@ mod remote_tests {
 		// create an ext without children keys
 		let ext = Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				pallets: vec!["Proxy".to_owned()],
 				child_trie: false,
 				state_snapshot: Some(SnapshotConfig::new(CACHE)),
@@ -1378,6 +1386,7 @@ mod remote_tests {
 			.mode(Mode::OfflineOrElseOnline(
 				OfflineConfig { state_snapshot: SnapshotConfig::new(CACHE) },
 				OnlineConfig {
+					transport: endpoint().clone().into(),
 					pallets: vec!["Proxy".to_owned()],
 					child_trie: false,
 					state_snapshot: Some(SnapshotConfig::new(CACHE)),
@@ -1419,6 +1428,7 @@ mod remote_tests {
 		init_logger();
 		Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				pallets: vec!["Proxy".to_owned()],
 				child_trie: false,
 				..Default::default()
@@ -1434,6 +1444,7 @@ mod remote_tests {
 		init_logger();
 		Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				pallets: vec!["Proxy".to_owned(), "Multisig".to_owned()],
 				child_trie: false,
 				..Default::default()
@@ -1451,6 +1462,7 @@ mod remote_tests {
 
 		Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				state_snapshot: Some(SnapshotConfig::new(CACHE)),
 				pallets: vec!["Proxy".to_owned()],
 				child_trie: false,
@@ -1480,6 +1492,7 @@ mod remote_tests {
 		init_logger();
 		Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
+				transport: endpoint().clone().into(),
 				state_snapshot: Some(SnapshotConfig::new(CACHE)),
 				pallets: vec!["Crowdloan".to_owned()],
 				child_trie: true,
@@ -1511,7 +1524,7 @@ mod remote_tests {
 		init_logger();
 		Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
-				transport: std::option_env!("TEST_WS").unwrap().to_owned().into(),
+				transport: endpoint().clone().into(),
 				pallets: vec!["Staking".to_owned()],
 				child_trie: false,
 				..Default::default()
@@ -1530,7 +1543,7 @@ mod remote_tests {
 		init_logger();
 		Builder::<Block>::new()
 			.mode(Mode::Online(OnlineConfig {
-				transport: std::option_env!("TEST_WS").unwrap().to_owned().into(),
+				transport: endpoint().clone().into(),
 				..Default::default()
 			}))
 			.build()
@@ -1543,9 +1556,10 @@ mod remote_tests {
 	async fn can_fetch_in_parallel() {
 		init_logger();
 
-		let uri = String::from("wss://kusama-bridge-hub-rpc.polkadot.io:443");
-		let mut builder = Builder::<Block>::new()
-			.mode(Mode::Online(OnlineConfig { transport: uri.into(), ..Default::default() }));
+		let mut builder = Builder::<Block>::new().mode(Mode::Online(OnlineConfig {
+			transport: endpoint().clone().into(),
+			..Default::default()
+		}));
 		builder.init_remote_client().await.unwrap();
 
 		let at = builder.as_online().at.unwrap();