Fix solo to para custom header return (#882)

* Adds an integration test for testing the migration

* Fix the custom validation header use case

test/service/tests/full_node_catching_up.rs

@@ -19,7 +19,7 @@ use cumulus_test_service::{initial_head_data, run_relay_chain_validator_node, Ke
 
 #[substrate_test_utils::test]
 #[ignore]
-async fn test_collating_and_non_collator_mode_catching_up() {
+async fn test_full_node_catching_up() {
 	let mut builder = sc_cli::LoggerBuilder::new("");
 	builder.with_colors(false);
 	let _ = builder.init();

test/service/tests/migrate_solo_to_para.rs

@@ -0,0 +1,111 @@
+// Copyright 2020-2021 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Test migration from parachain A to parachain B by returning the header of parachain B.
+//!
+//! This can be seen as a test of the fundamentals of the solo to parachain migration use case.
+//! The prerequisite is to have a running solo chain and a running parachain. The idea is that
+//! the solo chain is being stopped at a given point and sends its last header to the running parachain.
+//! The parachain will return this header as part of the validation phase on the relay chain to enact
+//! this header as its current latest state. As the old running parachain doesn't know this header, it will
+//! stop to produce new blocks. However, the old solo chain can now produce blocks using the parachain slot.
+//! (Be aware, that this is just a highlevel description and some parts are omitted.)
+
+use codec::Encode;
+use cumulus_primitives_core::ParaId;
+use cumulus_test_service::{initial_head_data, run_relay_chain_validator_node, Keyring::*};
+use sc_client_api::{BlockBackend, UsageProvider};
+use sp_runtime::generic::BlockId;
+
+#[substrate_test_utils::test]
+#[ignore]
+async fn test_migrate_solo_to_para() {
+	let mut builder = sc_cli::LoggerBuilder::new("");
+	builder.with_colors(false);
+	let _ = builder.init();
+
+	let para_id = ParaId::from(100);
+
+	let tokio_handle = tokio::runtime::Handle::current();
+
+	// start alice
+	let alice = run_relay_chain_validator_node(tokio_handle.clone(), Alice, || {}, Vec::new());
+
+	// start bob
+	let bob =
+		run_relay_chain_validator_node(tokio_handle.clone(), Bob, || {}, vec![alice.addr.clone()]);
+
+	// register parachain
+	alice
+		.register_parachain(
+			para_id,
+			cumulus_test_runtime::WASM_BINARY
+				.expect("You need to build the WASM binary to run this test!")
+				.to_vec(),
+			initial_head_data(para_id),
+		)
+		.await
+		.unwrap();
+
+	// run the parachain that will be used to return the header of the solo chain.
+	let parachain =
+		cumulus_test_service::TestNodeBuilder::new(para_id, tokio_handle.clone(), Charlie)
+			.enable_collator()
+			.connect_to_relay_chain_nodes(vec![&alice, &bob])
+			.build()
+			.await;
+
+	// run the solo chain (in our case this is also already a parachain, but as it has a different genesis it will not produce any blocks.)
+	let solo = cumulus_test_service::TestNodeBuilder::new(para_id, tokio_handle, Dave)
+		.enable_collator()
+		.connect_to_relay_chain_nodes(vec![&alice, &bob])
+		// Set some random value in the genesis state to create a different genesis hash.
+		.update_storage_parachain(|| {
+			sp_io::storage::set(b"test", b"test");
+		})
+		.build()
+		.await;
+
+	parachain.wait_for_blocks(2).await;
+
+	// Ensure that both chains have a different genesis hash.
+	assert_ne!(
+		parachain.client.block_hash(0).ok().flatten().unwrap(),
+		solo.client.block_hash(0).ok().flatten().unwrap(),
+	);
+
+	let solo_chain_header = solo.client.header(&BlockId::Number(0)).ok().flatten().unwrap();
+
+	// Send the transaction to set the custom header, aka the header of the solo chain.
+	parachain
+		.send_extrinsic(
+			cumulus_test_runtime::TestPalletCall::set_custom_validation_head_data {
+				custom_header: solo_chain_header.encode(),
+			},
+			Alice,
+		)
+		.await
+		.unwrap();
+
+	// Wait until the solo chain produced a block now as a parachain.
+	solo.wait_for_blocks(1).await;
+
+	let parachain_best = parachain.client.usage_info().chain.best_number;
+
+	// Wait for some more blocks and check that the old parachain doesn't produced/imported any new blocks.
+	solo.wait_for_blocks(2).await;
+	assert_eq!(parachain_best, parachain.client.usage_info().chain.best_number);
+}