lntemp: after mining, sync to latest block

Ensure active nodes are synced to the latest block mined.

There are two scenarios where they might not be synced to the correct
block even when SyncedToChain is true:
  1. The backend may have rejected a newly mined block (e.g., see
     lightningnetwork#7241).
  2. The backend might not have fully processed the new blocks yet.

In either case SyncedToChain will (correctly) be true since the node is
indeed fully synced to the backend. This commit makes sure we detect
case 1 above, while making sure we continue to wait in case 2.

lntemp/harness.go

@@ -1291,7 +1291,8 @@ func (h *HarnessTest) MineBlocks(num uint32) []*wire.MsgBlock {
 	blocks := h.Miner.MineBlocksSlow(num)
 
 	// Make sure all the active nodes are synced.
-	h.AssertActiveNodesSynced()
+	bestBlock := blocks[len(blocks)-1]
+	h.AssertActiveNodesSyncedTo(bestBlock)
 
 	return blocks
 }
@@ -1318,7 +1319,8 @@ func (h *HarnessTest) MineBlocksAndAssertNumTxes(num uint32,
 	}
 
 	// Finally, make sure all the active nodes are synced.
-	h.AssertActiveNodesSynced()
+	bestBlock := blocks[len(blocks)-1]
+	h.AssertActiveNodesSyncedTo(bestBlock)
 
 	return blocks
 }

lntemp/harness_assertion.go

@@ -39,6 +39,29 @@ func (h *HarnessTest) WaitForBlockchainSync(hn *node.HarnessNode) {
 	require.NoError(h, err, "timeout waiting for blockchain sync")
 }
 
+// WaitForBlockchainSyncTo waits until the node is synced to bestBlock.
+func (h *HarnessTest) WaitForBlockchainSyncTo(hn *node.HarnessNode,
+	bestBlock *wire.MsgBlock) {
+
+	bestBlockHash := bestBlock.BlockHash().String()
+	err := wait.NoError(func() error {
+		resp := hn.RPC.GetInfo()
+		if resp.SyncedToChain {
+			if resp.BlockHash == bestBlockHash {
+				return nil
+			}
+
+			return fmt.Errorf("%s's backend is synced to the "+
+				"wrong block (expected=%s, actual=%s)",
+				hn.Name(), bestBlockHash, resp.BlockHash)
+		}
+
+		return fmt.Errorf("%s is not synced to chain", hn.Name())
+	}, DefaultTimeout)
+
+	require.NoError(h, err, "timeout waiting for blockchain sync")
+}
+
 // AssertPeerConnected asserts that the given node b is connected to a.
 func (h *HarnessTest) AssertPeerConnected(a, b *node.HarnessNode) {
 	err := wait.NoError(func() error {
@@ -1324,6 +1347,14 @@ func (h *HarnessTest) AssertActiveNodesSynced() {
 	}
 }
 
+// AssertActiveNodesSyncedTo asserts all active nodes have synced to the
+// provided bestBlock.
+func (h *HarnessTest) AssertActiveNodesSyncedTo(bestBlock *wire.MsgBlock) {
+	for _, node := range h.manager.activeNodes {
+		h.WaitForBlockchainSyncTo(node, bestBlock)
+	}
+}
+
 // AssertPeerNotConnected asserts that the given node b is not connected to a.
 func (h *HarnessTest) AssertPeerNotConnected(a, b *node.HarnessNode) {
 	err := wait.NoError(func() error {