beacon/blsync: Add comprehensive finality test coverage

beacon/blsync/block_sync_test.go

@@ -134,9 +134,189 @@ func TestBlockSync(t *testing.T) {
 	expHeadBlock(testBlock2)
 }
 
+// TestBlockSyncFinality tests the beacon block sync's handling of finality updates.
+//
+// Beacon chain finality works as follows:
+// - An "attested" header is the latest block that has been attested to by validators
+// - A "finalized" header is a block that has been finalized (cannot be reverted)
+// - ChainHeadEvents should include the finalized block hash when finality data is available
+// - This enables the execution client to know which blocks are safe from reorgs
+func TestBlockSyncFinality(t *testing.T) {
+	ht := &testHeadTracker{}
+	blockSync := newBeaconBlockSync(ht)
+	headCh := make(chan types.ChainHeadEvent, 16)
+	blockSync.SubscribeChainHead(headCh)
+	ts := sync.NewTestScheduler(t, blockSync)
+	ts.AddServer(testServer1, 1)
+	ts.AddServer(testServer2, 1)
+
+	// expChainHeadEvent is a helper function that validates ChainHeadEvent emissions.
+	// It checks that:
+	// 1. An event is emitted when expected (or not emitted when expHead is nil)
+	// 2. The event contains the correct execution block number
+	// 3. The event contains the expected finalized hash (or empty hash when no finality)
+	expChainHeadEvent := func(expHead *types.BeaconBlock, expFinalizedHash common.Hash) {
+		t.Helper()
+		var event types.ChainHeadEvent
+		var hasEvent bool
+		select {
+		case event = <-headCh:
+			hasEvent = true
+		default:
+		}
+
+		if expHead == nil {
+			if hasEvent {
+				t.Errorf("Expected no chain head event, but got one with block number %d", event.Block.NumberU64())
+			}
+			return
+		}
+
+		if !hasEvent {
+			t.Errorf("Expected chain head event with block number %d, but got none", expHead.Header().Slot)
+			return
+		}
+
+		expPayload, err := expHead.ExecutionPayload()
+		if err != nil {
+			t.Fatalf("expHead.ExecutionPayload() failed: %v", err)
+		}
+
+		if event.Block.NumberU64() != expPayload.NumberU64() {
+			t.Errorf("Wrong head block number, expected %d, got %d", expPayload.NumberU64(), event.Block.NumberU64())
+		}
+
+		if event.Finalized != expFinalizedHash {
+			t.Errorf("Wrong finalized hash, expected %x, got %x", expFinalizedHash, event.Finalized)
+		}
+	}
+
+	// ═══════════════════════════════════════════════════════════════════════════════════
+	// Test Scenario 1: Basic finality with proper finality update
+	// ═══════════════════════════════════════════════════════════════════════════════════
+	// This tests the normal case where we have both an attested block (testBlock1) and
+	// a finalized block (testBlock2). The ChainHeadEvent should include the finalized
+	// block's execution hash, indicating to the execution client that testBlock2 is safe.
+
+	head1 := blockHeadInfo(testBlock1)
+	ht.prefetch = head1
+	ht.validated.Header = testBlock1.Header()
+
+	// Configure finality update: testBlock1 is attested, testBlock2 is finalized
+	ht.finalized.Attested.Header = testBlock1.Header()
+	ht.finalized.Finalized.Header = testBlock2.Header()
+	ht.finalized.Finalized.PayloadHeader = createTestExecutionHeader(testBlock2)
+
+	// Simulate the block sync process
+	ts.ServerEvent(sync.EvNewHead, testServer1, head1)
+	ts.Run(1, testServer1, sync.ReqBeaconBlock(head1.BlockRoot))
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 1), testBlock1)
+	ts.AddAllowance(testServer1, 1)
+	ts.Run(2)
+
+	// Verify that ChainHeadEvent includes the finalized block's execution hash
+	finalizedPayload, err := testBlock2.ExecutionPayload()
+	if err != nil {
+		t.Fatalf("Failed to get finalized payload: %v", err)
+	}
+	expFinalizedHash := finalizedPayload.Hash()
+	expChainHeadEvent(testBlock1, expFinalizedHash)
+
+	// ═══════════════════════════════════════════════════════════════════════════════════
+	// Test Scenario 2: No finality update available
+	// ═══════════════════════════════════════════════════════════════════════════════════
+	// This tests the case where we have a new head block but no finality information.
+	// The ChainHeadEvent should be emitted but with an empty finalized hash.
+
+	// Clear any pending events from the previous test
+	select {
+	case <-headCh:
+	default:
+	}
+
+	// Set up scenario: new head (testBlock2) but no finality update
+	ht.validated.Header = testBlock2.Header()
+	ht.finalized = types.FinalityUpdate{} // Explicitly clear finality data
+	head2 := blockHeadInfo(testBlock2)
+	ht.prefetch = head2
+
+	// Simulate block sync process
+	ts.ServerEvent(sync.EvNewHead, testServer1, head2)
+	ts.Run(3, testServer1, sync.ReqBeaconBlock(head2.BlockRoot))
+	ts.RequestEvent(request.EvResponse, ts.Request(3, 1), testBlock2)
+	ts.AddAllowance(testServer1, 1)
+	ts.Run(4)
+
+	// Verify ChainHeadEvent is emitted but with empty finalized hash
+	expChainHeadEvent(testBlock2, common.Hash{})
+
+	// ═══════════════════════════════════════════════════════════════════════════════════
+	// Test Scenario 3: Direct ValidatedFinality method testing
+	// ═══════════════════════════════════════════════════════════════════════════════════
+	// This tests the ValidatedFinality method directly to ensure it returns the correct
+	// finality update structure and availability flag.
+
+	// Clear any pending events
+	select {
+	case <-headCh:
+	default:
+	}
+
+	// Set up a proper finality update structure
+	ht.validated.Header = testBlock1.Header()
+	ht.finalized.Attested.Header = testBlock1.Header()
+	ht.finalized.Finalized.Header = testBlock2.Header()
+	ht.finalized.Finalized.PayloadHeader = createTestExecutionHeader(testBlock2)
+
+	// Test the ValidatedFinality method directly
+	finalityUpdate, hasFinalityUpdate := ht.ValidatedFinality()
+	if !hasFinalityUpdate {
+		t.Error("Expected finality update to be available")
+	}
+
+	if finalityUpdate.Attested.Header != testBlock1.Header() {
+		t.Error("Finality update attested header doesn't match expected testBlock1")
+	}
+
+	if finalityUpdate.Finalized.Header != testBlock2.Header() {
+		t.Error("Finality update finalized header doesn't match expected testBlock2")
+	}
+
+	// Test that the sync logic properly uses this finality update
+	// Since testBlock1 is already in cache, we can just run the sync logic
+	ts.Run(5)
+
+	// Verify that the finality information is properly included in the ChainHeadEvent
+	expChainHeadEvent(testBlock1, expFinalizedHash)
+}
+
+// createTestExecutionHeader creates a minimal ExecutionHeader for testing purposes.
+//
+// In production, ExecutionHeaders contain many fields (parent hash, state root, receipts root, etc.)
+// but for testing beacon chain finality logic, we only need the block hash to verify that
+// the correct finalized block is referenced in ChainHeadEvents.
+//
+// This simplified approach allows us to test the finality propagation logic without
+// dealing with the complexity of constructing full execution payloads.
+func createTestExecutionHeader(block *types.BeaconBlock) *types.ExecutionHeader {
+	payload, err := block.ExecutionPayload()
+	if err != nil {
+		panic(err)
+	}
+	// Create a minimal ExecutionHeader with only the block hash populated
+	// This is sufficient for testing finality hash propagation
+	execHeader := &deneb.ExecutionPayloadHeader{
+		BlockHash: [32]byte(payload.Hash()),
+	}
+	return types.NewExecutionHeader(execHeader)
+}
+
+// testHeadTracker is a mock implementation of the HeadTracker interface for testing.
+// It allows tests to simulate different beacon chain states and finality conditions.
 type testHeadTracker struct {
-	prefetch  types.HeadInfo
-	validated types.SignedHeader
+	prefetch  types.HeadInfo       // The head info to return from PrefetchHead()
+	validated types.SignedHeader   // The validated header for optimistic updates
+	finalized types.FinalityUpdate // The finality update data for comprehensive finality testing
 }
 
 func (h *testHeadTracker) PrefetchHead() types.HeadInfo {
@@ -151,13 +331,33 @@ func (h *testHeadTracker) ValidatedOptimistic() (types.OptimisticUpdate, bool) {
 	}, h.validated.Header != (types.Header{})
 }
 
-// TODO add test case for finality
+// ValidatedFinality returns the most recent finality update if available.
+//
+// This method implements a two-tier approach:
+//  1. Primary: If explicit finality data is set (h.finalized), return it directly
+//  2. Fallback: For backward compatibility with existing tests, create a minimal
+//     finality update from the validated header
+//
+// The fallback ensures that existing tests continue to work while new tests
+// can take advantage of the more comprehensive finality testing capabilities.
 func (h *testHeadTracker) ValidatedFinality() (types.FinalityUpdate, bool) {
-	finalized := types.NewExecutionHeader(new(deneb.ExecutionPayloadHeader))
-	return types.FinalityUpdate{
-		Attested:      types.HeaderWithExecProof{Header: h.validated.Header},
-		Finalized:     types.HeaderWithExecProof{PayloadHeader: finalized},
-		Signature:     h.validated.Signature,
-		SignatureSlot: h.validated.SignatureSlot,
-	}, h.validated.Header != (types.Header{})
+	// Primary path: Return explicit finality data if available
+	if h.finalized.Attested.Header != (types.Header{}) {
+		return h.finalized, true
+	}
+
+	// Fallback path: Create minimal finality update for backward compatibility
+	// This ensures existing tests continue to work without modification
+	if h.validated.Header != (types.Header{}) {
+		finalized := types.NewExecutionHeader(new(deneb.ExecutionPayloadHeader))
+		return types.FinalityUpdate{
+			Attested:      types.HeaderWithExecProof{Header: h.validated.Header},
+			Finalized:     types.HeaderWithExecProof{PayloadHeader: finalized},
+			Signature:     h.validated.Signature,
+			SignatureSlot: h.validated.SignatureSlot,
+		}, true
+	}
+
+	// No finality data available
+	return types.FinalityUpdate{}, false
 }