Second multiple candidates per relay parent test

node/core/backing/src/tests/mod.rs

@@ -197,7 +197,7 @@ fn make_erasure_root(test: &TestState, pov: PoV) -> Hash {
 	erasure_coding::branches(&chunks).root()
 }
 
-#[derive(Default)]
+#[derive(Default, Clone)]
 struct TestCandidateBuilder {
 	para_id: ParaId,
 	head_data: HeadData,

node/core/backing/src/tests/prospective_parachains.rs

@@ -787,3 +787,134 @@ fn prospective_parachains_reject_candidate() {
 		virtual_overseer
 	});
 }
+
+// Test that a validator can second multiple candidates per single relay parent.
+#[test]
+fn second_multiple_candidates_per_relay_parent() {
+	let test_state = TestState::default();
+	test_harness(test_state.keystore.clone(), |mut virtual_overseer| async move {
+		// Candidate `a` is seconded in a parent of the activated `leaf`.
+		const LEAF_BLOCK_NUMBER: BlockNumber = 100;
+		const LEAF_DEPTH: BlockNumber = 3;
+		let para_id = test_state.chain_ids[0];
+
+		let leaf_hash = Hash::from_low_u64_be(130);
+		let leaf_parent = get_parent_hash(leaf_hash);
+		let leaf_grandparent = get_parent_hash(leaf_parent);
+		let activated = ActivatedLeaf {
+			hash: leaf_hash,
+			number: LEAF_BLOCK_NUMBER,
+			status: LeafStatus::Fresh,
+			span: Arc::new(jaeger::Span::Disabled),
+		};
+		let min_relay_parents = vec![(para_id, LEAF_BLOCK_NUMBER - LEAF_DEPTH)];
+		let test_leaf_a = TestLeaf { activated, min_relay_parents };
+
+		activate_leaf(&mut virtual_overseer, test_leaf_a, &test_state, 0).await;
+
+		let pov = PoV { block_data: BlockData(vec![42, 43, 44]) };
+		let pvd = dummy_pvd();
+		let validation_code = ValidationCode(vec![1, 2, 3]);
+
+		let expected_head_data = test_state.head_data.get(&para_id).unwrap();
+
+		let pov_hash = pov.hash();
+		let candidate_a = TestCandidateBuilder {
+			para_id,
+			relay_parent: leaf_parent,
+			pov_hash,
+			head_data: expected_head_data.clone(),
+			erasure_root: make_erasure_root(&test_state, pov.clone()),
+			persisted_validation_data_hash: pvd.hash(),
+			validation_code: validation_code.0.clone(),
+			..Default::default()
+		};
+		let mut candidate_b = candidate_a.clone();
+		candidate_b.relay_parent = leaf_grandparent;
+
+		// With depths.
+		let candidate_a = (candidate_a.build(), 1);
+		let candidate_b = (candidate_b.build(), 2);
+
+		for candidate in &[candidate_a, candidate_b] {
+			let (candidate, depth) = candidate;
+			let second = CandidateBackingMessage::Second(
+				leaf_hash,
+				candidate.to_plain(),
+				pvd.clone(),
+				pov.clone(),
+			);
+
+			virtual_overseer.send(FromOverseer::Communication { msg: second }).await;
+
+			assert_validate_seconded_candidate(
+				&mut virtual_overseer,
+				candidate.descriptor().relay_parent,
+				&candidate,
+				&pov,
+				&pvd,
+				&validation_code,
+				expected_head_data,
+			)
+			.await;
+
+			// `seconding_sanity_check`
+			let expected_request_a = vec![(
+				HypotheticalDepthRequest {
+					candidate_hash: candidate.hash(),
+					candidate_para: para_id,
+					parent_head_data_hash: pvd.parent_head.hash(),
+					candidate_relay_parent: candidate.descriptor().relay_parent,
+					fragment_tree_relay_parent: leaf_hash,
+				},
+				vec![*depth],
+			)];
+			assert_hypothetical_depth_requests(&mut virtual_overseer, expected_request_a.clone())
+				.await;
+
+			// Prospective parachains are notified.
+			assert_matches!(
+				virtual_overseer.recv().await,
+				AllMessages::ProspectiveParachains(
+					ProspectiveParachainsMessage::CandidateSeconded(
+						candidate_para,
+						candidate_receipt,
+						_pvd,
+						tx,
+					),
+				) if &candidate_receipt == candidate && candidate_para == para_id && pvd == _pvd => {
+					// Any non-empty response will do.
+					tx.send(vec![(leaf_hash, vec![0, 2, 3])]).unwrap();
+				}
+			);
+
+			test_dispute_coordinator_notifications(
+				&mut virtual_overseer,
+				candidate.hash(),
+				test_state.session(),
+				vec![ValidatorIndex(0)],
+			)
+			.await;
+
+			assert_matches!(
+				virtual_overseer.recv().await,
+				AllMessages::StatementDistribution(
+					StatementDistributionMessage::Share(
+						parent_hash,
+						_signed_statement,
+					)
+				) if parent_hash == candidate.descriptor().relay_parent => {}
+			);
+
+			assert_matches!(
+				virtual_overseer.recv().await,
+				AllMessages::CollatorProtocol(CollatorProtocolMessage::Seconded(hash, statement)) => {
+					assert_eq!(candidate.descriptor().relay_parent, hash);
+					assert_matches!(statement.payload(), Statement::Seconded(_));
+				}
+			);
+		}
+
+		virtual_overseer
+	});
+}