itest: test channel.backup changes upon shutdown

itest/lnd_channel_backup_test.go

@@ -786,8 +786,15 @@ func runChanRestoreScenarioForceClose(ht *lntest.HarnessTest, zeroConf bool) {
 	ht.AssertNumTxsInMempool(1)
 
 	// Now that we're able to make our restored now, we'll shutdown the old
-	// Dave node as we'll be storing it shortly below.
-	ht.Shutdown(dave)
+	// Dave node as we'll be storing it shortly below. Use SuspendNode, not
+	// Shutdown to keep its directory including channel.backup file.
+	ht.SuspendNode(dave)
+
+	// Read Dave's channel.backup file again to make sure it was updated
+	// upon Dave's shutdown.
+	multi2, err := os.ReadFile(backupFilePath)
+	require.NoError(ht, err)
+	require.NotEqual(ht, multi, multi2)
 
 	// Mine a block to confirm the closing tx from Dave.
 	ht.MineBlocksAndAssertNumTxes(1, 1)