Adding Bridges code as git subtree. (#2515)

* Add instructions.

* Squashed 'bridges/' content from commit 345e84a21

git-subtree-dir: bridges
git-subtree-split: 345e84a2146b56628e9888c9f5e129cb40e868a9

* Remove bridges workspace file to avoid confusing Cargo.

* Add some bridges primitives to Polkadot workspace.

* Improve docs.

polkadot/bridges/primitives/header-chain/tests/justification.rs

@@ -0,0 +1,114 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common 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.
+
+// Parity Bridges Common 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 Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Tests for Grandpa Justification code.
+
+use bp_header_chain::justification::{verify_justification, Error, GrandpaJustification};
+use bp_test_utils::*;
+use codec::Encode;
+
+type TestHeader = sp_runtime::testing::Header;
+
+fn make_justification_for_header_1() -> GrandpaJustification<TestHeader> {
+	make_justification_for_header(
+		&test_header(1),
+		TEST_GRANDPA_ROUND,
+		TEST_GRANDPA_SET_ID,
+		&authority_list(),
+	)
+}
+
+#[test]
+fn justification_with_invalid_encoding_rejected() {
+	assert_eq!(
+		verify_justification::<TestHeader>(header_id::<TestHeader>(1), TEST_GRANDPA_SET_ID, voter_set(), &[],),
+		Err(Error::JustificationDecode),
+	);
+}
+
+#[test]
+fn justification_with_invalid_target_rejected() {
+	assert_eq!(
+		verify_justification::<TestHeader>(
+			header_id::<TestHeader>(2),
+			TEST_GRANDPA_SET_ID,
+			voter_set(),
+			&make_justification_for_header_1().encode(),
+		),
+		Err(Error::InvalidJustificationTarget),
+	);
+}
+
+#[test]
+fn justification_with_invalid_commit_rejected() {
+	let mut justification = make_justification_for_header_1();
+	justification.commit.precommits.clear();
+
+	assert_eq!(
+		verify_justification::<TestHeader>(
+			header_id::<TestHeader>(1),
+			TEST_GRANDPA_SET_ID,
+			voter_set(),
+			&justification.encode(),
+		),
+		Err(Error::InvalidJustificationCommit),
+	);
+}
+
+#[test]
+fn justification_with_invalid_authority_signature_rejected() {
+	let mut justification = make_justification_for_header_1();
+	justification.commit.precommits[0].signature = Default::default();
+
+	assert_eq!(
+		verify_justification::<TestHeader>(
+			header_id::<TestHeader>(1),
+			TEST_GRANDPA_SET_ID,
+			voter_set(),
+			&justification.encode(),
+		),
+		Err(Error::InvalidAuthoritySignature),
+	);
+}
+
+#[test]
+fn justification_with_invalid_precommit_ancestry() {
+	let mut justification = make_justification_for_header_1();
+	justification.votes_ancestries.push(test_header(10));
+
+	assert_eq!(
+		verify_justification::<TestHeader>(
+			header_id::<TestHeader>(1),
+			TEST_GRANDPA_SET_ID,
+			voter_set(),
+			&justification.encode(),
+		),
+		Err(Error::InvalidPrecommitAncestries),
+	);
+}
+
+#[test]
+fn valid_justification_accepted() {
+	assert_eq!(
+		verify_justification::<TestHeader>(
+			header_id::<TestHeader>(1),
+			TEST_GRANDPA_SET_ID,
+			voter_set(),
+			&make_justification_for_header_1().encode(),
+		),
+		Ok(()),
+	);
+}