lnwallet: add test to execrise unconfirmed transcations notified by SubscribeTransactions

In this commit, we add a new test to ensure that all backends will
properly send out notifications when an unconfirmed transcation that we
send is inserted into the tx store. Before we updated the btcwallet
build commit in dep, this would fail for neutrino but now passes.

lnwallet/interface_test.go

@@ -1270,6 +1270,45 @@ func testTransactionSubscriptions(miner *rpctest.Harness,
 		t.Fatalf("transactions not received after 5 seconds")
 	case <-confirmedNtfns: // Fall through on success
 	}
+
+	// We'll also ensure that the client is able to send our new
+	// notifications when we _create_ transactions ourselves that spend our
+	// own outputs.
+	b := txscript.NewScriptBuilder()
+	b.AddOp(txscript.OP_0)
+	outputScript, err := b.Script()
+	if err != nil {
+		t.Fatalf("unable to make output script: %v", err)
+	}
+	burnOutput := wire.NewTxOut(outputAmt, outputScript)
+	txid, err := alice.SendOutputs([]*wire.TxOut{burnOutput}, 2500)
+	if err != nil {
+		t.Fatalf("unable to create burn tx: %v", err)
+	}
+	err = waitForMempoolTx(miner, txid)
+	if err != nil {
+		t.Fatalf("tx not relayed to miner: %v", err)
+	}
+
+	// Before we mine the next block, we'll ensure that the above
+	// transaction shows up in the set of unconfirmed transactions returned
+	// by ListTransactionDetails.
+	err = waitForWalletSync(miner, alice)
+	if err != nil {
+		t.Fatalf("Couldn't sync Alice's wallet: %v", err)
+	}
+
+	// As we just sent the transaction and it was landed in the mempool, we
+	// should get a notification for a new unconfirmed transactions
+	select {
+	case <-time.After(time.Second * 10):
+		t.Fatalf("transactions not received after 10 seconds")
+	case unConfTx := <-txClient.UnconfirmedTransactions():
+		if unConfTx.Hash != *txid {
+			t.Fatalf("wrong txn notified: expected %v got %v",
+				txid, unConfTx.Hash)
+		}
+	}
 }
 
 // testPublishTransaction checks that PublishTransaction returns the