tests: add a test for closing a channel with LND

Not sure if we should add this as the Dispose() method
of the test class actually:
https://stackoverflow.com/a/33516224/544947

src/BTCPayServer.Lightning.Common/OpenChannelResponse.cs

@@ -23,5 +23,9 @@ public OpenChannelResult Result
         {
             get; set;
         }
+        public string FundingTxIdIfAvailable
+        {
+            get; set;
+        }
     }
 }

src/BTCPayServer.Lightning.LND/LndClient.cs

@@ -373,7 +373,9 @@ async Task<OpenChannelResponse> ILightningClient.OpenChannel(OpenChannelRequest
                     req.Sat_per_byte = ((int)openChannelRequest.FeeRate.SatoshiPerByte).ToString();
                 }
                 var result = await this.SwaggerClient.OpenChannelSyncAsync(req, cancellation);
-                return new OpenChannelResponse(OpenChannelResult.Ok);
+                var res = new OpenChannelResponse(OpenChannelResult.Ok);
+                res.FundingTxIdIfAvailable = result.Funding_txid_str;
+                return res;
             }
             catch(SwaggerException ex) when
                 (ex.AsLNDError() is LndError2 lndError &&

tests/ChannelSetup.cs

@@ -48,6 +48,15 @@ public static async Task OpenAll(RPCClient cashCow, IEnumerable<ILightningClient
                 }
             }
         }
+
+        private static Dictionary<(ILightningClient, ILightningClient), string> availableFundingTxIds
+            = new Dictionary<(ILightningClient, ILightningClient), string>();
+
+        internal static string GetFundingTxIdForChannel(ILightningClient sender, ILightningClient dest)
+        {
+            return availableFundingTxIds.GetValueOrDefault((sender, dest));
+        }
+
         public static async Task OpenChannel(RPCClient cashCow, ILightningClient sender, ILightningClient dest)
         {
             var destInfo = await dest.GetInfo();
@@ -115,6 +124,8 @@ public static async Task OpenChannel(RPCClient cashCow, ILightningClient sender,
                     }
                     if(openChannel.Result == OpenChannelResult.Ok)
                     {
+                        if (!String.IsNullOrEmpty(openChannel.FundingTxIdIfAvailable))
+                            availableFundingTxIds[(sender, dest)] = openChannel.FundingTxIdIfAvailable;
                         // generate one block and a bit more time to confirm channel opening
                         await cashCow.GenerateAsync(1);
                         await WaitLNSynched(cashCow, sender);

tests/CommonTests.cs

@@ -536,5 +536,30 @@ public void CanParseLightningURL()
 			Assert.True(LightningConnectionString.TryParse("type=charge;server=http://api-token:[email protected]:54938/;allowinsecure=true", out conn));
 			Assert.Equal("type=charge;server=http://127.0.0.1:54938/;api-token=foiewnccewuify;allowinsecure=true", conn.ToString());
 		}
+
+		[Fact(Timeout = Timeout)]
+		public async Task CanCloseLndChannel()
+		{
+			// TODO: test in all LN implementations, not just LND
+			//foreach (var test in Tester.GetTestedPairs())
+			//{
+				var test = Tester.GetTestedLndPair();
+				await EnsureConnectedToDestinations(test);
+				var customer = (ILightningClient)test.Customer;
+				var senderChannel = (await customer.ListChannels()).First();
+
+				var senderInfo = await customer.GetInfo();
+				var fundingTxIdForChannel = ChannelSetup.GetFundingTxIdForChannel(customer, test.Merchant);
+				if (String.IsNullOrEmpty(fundingTxIdForChannel))
+					throw new InvalidOperationException("Could not find funding Tx ID of channel");
+				var closeChannelRequest = new CloseChannelRequest()
+				{
+					NodeInfo = senderInfo.NodeInfoList.First(),
+					ChannelPointOutputIndex = senderChannel.ChannelPoint.N,
+					ChannelPointFundingTxIdStr = fundingTxIdForChannel
+				};
+				await test.Merchant.CloseChannel(closeChannelRequest, CancellationToken.None);
+			//}
+		}
 	}
 }

tests/Tester.cs

@@ -87,11 +87,18 @@ public static LndClient CreateLndClientDest()
 			yield return ("Eclair (Client)", CreateEclairClient());
 		}
 
+		private static (string Name, ILightningClient Customer, ILightningClient Merchant) GetTestedCLightningPair()
+			=> ("C-Lightning", CreateCLightningClient(), CreateCLightningClientDest());
+		internal static (string Name, LndClient Customer, LndClient Merchant) GetTestedLndPair()
+			=> ("LND", CreateLndClient(), CreateLndClientDest());
+		private static (string Name, ILightningClient Customer, ILightningClient Merchant) GetTestedEclairPair()
+			=> ("Eclair", CreateEclairClient(), CreateEclairClientDest());
+
 		public static IEnumerable<(string Name, ILightningClient Customer, ILightningClient Merchant)> GetTestedPairs()
 		{
-			yield return ("C-Lightning", CreateCLightningClient(), CreateCLightningClientDest());
-			yield return ("LND", CreateLndClient(), CreateLndClientDest());
-			yield return ("Eclair", CreateEclairClient(), CreateEclairClientDest());
+			yield return GetTestedCLightningPair();
+			yield return GetTestedLndPair();
+			yield return GetTestedEclairPair();
 		}
 	}
 }