lntest+itest: fix flakes found using neutrino backend

This commit makes sure the sweep requests are received before mining
blocks to trigger the actual sweeping.

In addition, `testFundingExpiryBlocksOnPending` is updated to deal with
the old `channel link not found` issue.

itest/lnd_funding_test.go

@@ -12,7 +12,6 @@ import (
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/chainreg"
-	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/funding"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/labels"
@@ -1341,22 +1340,22 @@ func testChannelFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	// that by dave force-closing the channel. Which let's carol sweep its
 	// to_remote output which is not encumbered by any relative locktime.
 	ht.CloseChannelAssertPending(dave, chanPoint2, true)
+
 	// Mine the force close commitment transaction.
 	ht.MineBlocksAndAssertNumTxes(1, 1)
 
+	// Make sure Carol sees her to_remote output from the force close tx.
+	ht.AssertNumPendingSweeps(carol, 1)
+
 	// Mine one block to trigger the sweep transaction.
 	ht.MineEmptyBlocks(1)
 
 	// We need to wait for carol initiating the sweep of the to_remote
 	// output of chanPoint2.
-	utxos := ht.AssertNumUTXOsUnconfirmed(carol, 1)
+	utxo := ht.AssertNumUTXOsUnconfirmed(carol, 1)[0]
 
-	// We filter for the unconfirmed utxo and try to open a channel with
+	// We now try to open channel using the unconfirmed utxo.
-	// that utxo.
+	fundingUtxo := utxo
-	utxoOpt := fn.Find(func(u *lnrpc.Utxo) bool {
-		return u.Confirmations == 0
-	}, utxos)
-	fundingUtxo := utxoOpt.UnwrapOrFail(ht.T)
 
 	// Now try to open the channel with this utxo and expect an error.
 	expectedErr := fmt.Errorf("outpoint already spent or "+
@@ -1405,6 +1404,9 @@ func testChannelFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	ht.CloseChannelAssertPending(dave, chanPoint3, true)
 	ht.MineBlocksAndAssertNumTxes(1, 1)
 
+	// Make sure Carol sees her to_remote output from the force close tx.
+	ht.AssertNumPendingSweeps(carol, 1)
+
 	// Mine one block to trigger the sweep transaction.
 	ht.MineEmptyBlocks(1)
 

itest/lnd_open_channel_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -767,6 +768,18 @@ func testFundingExpiryBlocksOnPending(ht *lntest.HarnessTest) {
 	// channel.
 	ht.MineBlocksAndAssertNumTxes(1, 1)
 	chanPoint := lntest.ChanPointFromPendingUpdate(update)
+
+	// TODO(yy): remove the sleep once the following bug is fixed.
+	//
+	// We may get the error `unable to gracefully close channel
+	// while peer is offline (try force closing it instead):
+	// channel link not found`. This happens because the channel
+	// link hasn't been added yet but we now proceed to closing the
+	// channel. We may need to revisit how the channel open event
+	// is created and make sure the event is only sent after all
+	// relevant states have been updated.
+	time.Sleep(2 * time.Second)
+
 	ht.CloseChannel(alice, chanPoint)
 }
 

itest/lnd_psbt_test.go

@@ -1683,6 +1683,9 @@ func testPsbtChanFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	ht.CloseChannelAssertPending(dave, channelPoint, true)
 	ht.MineBlocksAndAssertNumTxes(1, 1)
 
+	// Make sure Carol sees her to_remote output from the force close tx.
+	ht.AssertNumPendingSweeps(carol, 1)
+
 	// Mine one block to trigger the sweep transaction.
 	ht.MineEmptyBlocks(1)
 
@@ -1805,6 +1808,9 @@ func testPsbtChanFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	ht.CloseChannelAssertPending(dave, channelPoint2, true)
 	ht.MineBlocksAndAssertNumTxes(1, 1)
 
+	// Make sure Carol sees her to_remote output from the force close tx.
+	ht.AssertNumPendingSweeps(carol, 1)
+
 	// Mine one block to trigger the sweep transaction.
 	ht.MineEmptyBlocks(1)
 
@@ -1929,12 +1935,6 @@ func testPsbtChanFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	updateResp = ht.ReceiveOpenChannelUpdate(chanUpdates)
 	upd, ok = updateResp.Update.(*lnrpc.OpenStatusUpdate_ChanPending)
 	require.True(ht, ok)
-	channelPoint3 := &lnrpc.ChannelPoint{
-		FundingTxid: &lnrpc.ChannelPoint_FundingTxidBytes{
-			FundingTxidBytes: upd.ChanPending.Txid,
-		},
-		OutputIndex: upd.ChanPending.OutputIndex,
-	}
 
 	err = finalTx.Deserialize(bytes.NewReader(finalizeRes.RawFinalTx))
 	require.NoError(ht, err)
@@ -1942,6 +1942,4 @@ func testPsbtChanFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	txHash = finalTx.TxHash()
 	block = ht.MineBlocksAndAssertNumTxes(1, 1)[0]
 	ht.AssertTxInBlock(block, &txHash)
-
-	ht.CloseChannel(carol, channelPoint3)
 }

lntest/harness_assertion.go

@@ -785,8 +785,13 @@ func (h *HarnessTest) AssertNumUTXOsWithConf(hn *node.HarnessNode,
 			return nil
 		}
 
+		desc := "has UTXOs:\n"
+		for _, utxo := range resp.Utxos {
+			desc += fmt.Sprintf("%v\n", utxo)
+		}
+
 		return errNumNotMatched(hn.Name(), "num of UTXOs",
-			expectedUtxos, total-old, total, old)
+			expectedUtxos, total-old, total, old, desc)
 	}, DefaultTimeout)
 	require.NoError(h, err, "timeout waiting for UTXOs")
 

lntest/utils.go

@@ -53,10 +53,16 @@ func CopyFile(dest, src string) error {
 
 // errNumNotMatched is a helper method to return a nicely formatted error.
 func errNumNotMatched(name string, subject string,
-	want, got, total, old int) error {
+	want, got, total, old int, desc ...any) error {
 
-	return fmt.Errorf("%s: assert %s failed: want %d, got: %d, total: "+
+	err := fmt.Errorf("%s: assert %s failed: want %d, got: %d, total: "+
 		"%d, previously had: %d", name, subject, want, got, total, old)
+
+	if len(desc) > 0 {
+		err = fmt.Errorf("%w, desc: %v", err, desc)
+	}
+
+	return err
 }
 
 // parseDerivationPath parses a path in the form of m/x'/y'/z'/a/b into a slice