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

@@ -0,0 +1,66 @@
+// 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/>.
+
+use cumulus_primitives_core::ParaId;
+use cumulus_test_service::{initial_head_data, run_relay_chain_validator_node, Keyring::*};
+
+#[substrate_test_utils::test]
+#[ignore]
+async fn test_full_node_catching_up() {
+	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 cumulus charlie (a parachain collator)
+	let charlie =
+		cumulus_test_service::TestNodeBuilder::new(para_id, tokio_handle.clone(), Charlie)
+			.enable_collator()
+			.connect_to_relay_chain_nodes(vec![&alice, &bob])
+			.build()
+			.await;
+	charlie.wait_for_blocks(5).await;
+
+	// run cumulus dave (a parachain full node) and wait for it to sync some blocks
+	let dave = cumulus_test_service::TestNodeBuilder::new(para_id, tokio_handle, Dave)
+		.connect_to_parachain_node(&charlie)
+		.connect_to_relay_chain_nodes(vec![&alice, &bob])
+		.build()
+		.await;
+	dave.wait_for_blocks(7).await;
+}