works!

.vscode/launch.json

@@ -1,6 +1,8 @@
 {
     "version": "0.2.0",
     "configurations": [
+
+
     
         {
             // Use IntelliSense to find out which attributes exist for C# debugging
@@ -12,7 +14,7 @@
             "preLaunchTask": "build",
             // If you have changed target frameworks, make sure to update the program path.
             "program": "${workspaceFolder}/bin/Debug/net7.0/DemoApplication.dll",
-            "args": [],
+            "args": ["-f", "assets/input1.json", "-f", "assets/input2.json", "out.csv"],
             "cwd": "${workspaceFolder}",
             // For more information about the 'console' field, see https://aka.ms/VSCode-CS-LaunchJson-Console
             "console": "internalConsole",

assets/input1.json

@@ -1,6 +1,6 @@
 {
 	"OrderId": 1,
-	"Description": " Order 123",
+	"Description": "Order 123",
 	"customer ID": 123,
 	"products": [{
 			"ProductId": "PID1",

assets/input2.json

@@ -1,6 +1,6 @@
 {
 	"OrderId": 3,
-	"Description": " Order 11234",
+	"Description": "Order 11234",
 	"customer ID": 1134,
 	"products": [{
 			"ProductId": "PID3",

models/OrderModel.cs

@@ -10,7 +10,7 @@ public sealed class OrderModel {
 
     public OrderModel(OrderDto orderDTO) {
         OrderId = orderDTO.OrderId;
-        OrderDescription = orderDTO.Description;
+        OrderDescription = orderDTO.Description.Trim();
         CustomerId = orderDTO.CustomerId;
         TotalPrice = orderDTO.Products.Select(product => product.Price).Sum();
     }

services/CsvWriter.cs

@@ -8,6 +8,7 @@ class CsvFileWriter
 
     public CsvFileWriter(FileInfo fileInfo) {
         textWriter = new StreamWriter(fileInfo.FullName);
+        
         csvWriter = new CsvWriter(textWriter, CultureInfo.InvariantCulture);
     }
 
@@ -17,6 +18,7 @@ class CsvFileWriter
         csvWriter.WriteField(orderModel.CustomerId);
         csvWriter.WriteField(orderModel.TotalPrice);
 
+        csvWriter.Flush();
         csvWriter.NextRecord();
     }
 }

services/DemoApplicationConfiguration.cs

@@ -30,14 +30,15 @@ namespace Configuration
             var outputFileName = new FileInfo(args.Last());
 
             // Remove last file-name arg, to get a more consistent array
-            args = args.SkipLast(1).ToArray();
+            var strippedArgs = args.SkipLast(1).ToArray();
 
 
-            string[] givenFlags = args.Where((value, index) => index % 2 == 0).ToArray();
-            string[] givenFilePaths = args.Where((value, index) => index % 2 != 0).ToArray();
+            string[] givenFlags = strippedArgs.Where((value, index) => index % 2 == 0).ToArray();
+            string[] givenFilePaths = strippedArgs.Where((value, index) => index % 2 != 0).ToArray();
             
             try
             {
+                // Assert only a single 'd' was passed
                 if ( givenFlags.Length == 1 && givenFlags[0].Equals("-d") ) {
                 string[] filesInDirectory = Directory.GetFiles(givenFilePaths[0]);
                 return new DemoApplicationConfiguration {
@@ -45,6 +46,7 @@ namespace Configuration
                     JsonFilesInfo = filesInDirectory.Select(name => new FileInfo(name)).ToArray(),
                 };
             }
+                // Assert only '-f' were passed
                 else if (givenFlags.All((string flag) => flag.Equals("-f"))) {
                     return new DemoApplicationConfiguration {
                         OutputFile = outputFileName,
@@ -52,12 +54,11 @@ namespace Configuration
                     };
                 }
                 else {
-                    throw new DemoApplicationConfigurationException("Must have either 1 flag that is '-d', of all flags must be '-f");
+                    throw new DemoApplicationConfigurationException("Must have either 1 flag that is '-d', or all flags must be '-f");
                 }
-            }
-            catch (System.Exception e)
+            } catch (Exception)
             {
-                Console.WriteLine("Something else went wrong");
+                Console.WriteLine("Something went wrong");
                 throw;
             }
         }