itest: document missing wallet UTXO

itest/flakes.go

@@ -3,7 +3,9 @@ package itest
 import (
 	"time"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/lightningnetwork/lnd/lntest"
+	"github.com/lightningnetwork/lnd/lntest/node"
 )
 
 // flakePreimageSettlement documents a flake found when testing the preimage
@@ -31,3 +33,16 @@ func flakePreimageSettlement(ht *lntest.HarnessTest) {
 	// would cause the sweeper to RBF it.
 	time.Sleep(2 * time.Second)
 }
+
+// flakeFundExtraUTXO documents a flake found when testing the sweeping behavior
+// of the given node, which would fail due to no wallet UTXO available, while
+// there should be enough.
+//
+// TODO(yy): remove it once the issue is resolved.
+func flakeFundExtraUTXO(ht *lntest.HarnessTest, node *node.HarnessNode) {
+	// The node should have enough wallet UTXOs here to sweep the HTLC in
+	// the end of this test. However, due to a known issue, the node's
+	// wallet may report there's no UTXO available. For details,
+	// - https://github.com/lightningnetwork/lnd/issues/8786
+	ht.FundCoins(btcutil.SatoshiPerBitcoin, node)
+}