Address comments

VSConfigFinder.Test/.editorconfig

@@ -118,6 +118,8 @@ dotnet_style_allow_statement_immediately_after_block_experimental = true:silent
 
 # Diagnostics
 
+# CS8602: Dereference of a possibly null reference.
+dotnet_diagnostic.CS8602.severity = error
 # CS8603: Possible null reference return.
 dotnet_diagnostic.CS8603.severity = error
 dotnet_style_namespace_match_folder = true:suggestion

VSConfigFinder.Test/UtilitiesTests.cs

@@ -5,6 +5,9 @@
 
 namespace VSConfigFinder.Test
 {
+    using Moq;
+    using System.Text;
+    using System.Text.Json;
     using Xunit;
 
     public class UtilitiesTests
@@ -25,5 +28,97 @@ public void ValidateIsNotNullOrEmpty_NotNullOrEmpty_String_Succeeds()
             var str = "some string";
             Utilities.ValidateIsNotNullOrEmpty(str, nameof(str));
         }
+
+        [Fact]
+        public void CreateOutput_Creates_File_With_Expected_String()
+        {
+            var fileSystem = new Mock<IFileSystem>();
+            var finalConfig = new VSConfig
+            {
+                Version = new Version("1.0"),
+                Components = new[]
+                {
+                    "Microsoft.VisualStudio.Component.NuGet",
+                    "Microsoft.VisualStudio.Component.Roslyn.Compiler",
+                    "Microsoft.Component.MSBuild",
+                    "Microsoft.NetCore.Component.Runtime.6.0"
+                },
+            };
+
+            var jsonString = """
+                {
+                  "Version": "1.0",
+                  "Components": [
+                    "Microsoft.VisualStudio.Component.NuGet",
+                    "Microsoft.VisualStudio.Component.Roslyn.Compiler",
+                    "Microsoft.Component.MSBuild",
+                    "Microsoft.NetCore.Component.Runtime.6.0"
+                  ]
+                }
+                """;
+
+            var options = new CommandLineOptions
+            {
+                FolderPath = "C:\\input",
+                CreateFile = true,
+                ConfigOutputPath = "C:\\output",
+            };
+
+            Utilities.CreateOutput(fileSystem.Object, finalConfig, options);
+
+            var outputPath = Path.Combine(options.ConfigOutputPath, ".vsconfig");
+            fileSystem.Verify(x => x.WriteAllText(outputPath, jsonString));
+        }
+
+        [Fact]
+        public void ReadComponents_Reads_AllNestedDirectories_And_OutputsAllComponents()
+        {
+            var fileSystem = new Mock<IFileSystem>();
+
+            var options = new CommandLineOptions
+            {
+                FolderPath = "C:\\input",
+                ConfigOutputPath = "C:\\output",
+            };
+
+            // pathA
+            var pathA = "C:\\pathA";
+            var pathAConfig = """
+                {
+                  "Version": "1.0",
+                  "Components": [
+                    "Microsoft.VisualStudio.Component.NuGet",
+                    "Microsoft.Component.MSBuild",
+                  ]
+                }
+                """;
+            var pathAReader = new MemoryStream(Encoding.UTF8.GetBytes(pathAConfig));
+
+            // pathB
+            var pathB = "C:\\pathB";
+            var pathBConfig = """
+                {
+                  "Version": "1.0",
+                  "Components": [
+                    "Microsoft.VisualStudio.Component.NuGet",
+                    "Microsoft.VisualStudio.Component.Roslyn.Compiler",
+                  ]
+                }
+                """;
+            var pathBReader = new MemoryStream(Encoding.UTF8.GetBytes(pathBConfig));
+
+            fileSystem.Setup(x => x.GetFileSystemEntries(options.FolderPath, ".vsconfig", true)).Returns(new[] { pathA, pathB });
+
+            fileSystem.Setup(x => x.OpenFile(pathA)).Returns(pathAReader);
+            fileSystem.Setup(x => x.OpenFile(pathB)).Returns(pathBReader);
+
+            var components = Utilities.ReadComponents(fileSystem.Object, options);
+            Assert.Equal(3, components.Length);
+            Assert.Collection(
+                components,
+                x => Assert.Equal("Microsoft.VisualStudio.Component.NuGet", x),
+                x => Assert.Equal("Microsoft.Component.MSBuild", x),
+                x => Assert.Equal("Microsoft.VisualStudio.Component.Roslyn.Compiler", x));
+        }
     }
 }

VSConfigFinder.Test/VSConfigFinder.Test.csproj

@@ -10,6 +10,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
+    <PackageReference Include="Moq" Version="4.18.4" />
     <PackageReference Include="xunit" Version="2.4.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

VSConfigFinder/.editorconfig

@@ -1,4 +1,4 @@
-file_header_template = <copyright file="{fileName}" company="Microsoft Corporation">\nCopyright (C) Microsoft Corporation. All rights reserved.\nLicensed under the MIT license. See LICENSE.txt in the project root for license information.\n</copyright>
+file_header_template = <copyright file="{fileName}" company="Microsoft Corporation">\nCopyright (C) Microsoft Corporation. All rights reserved.\nLicensed under the MIT license. See LICENSE.txt in the project root for license information.\n</copyright>
 
 # All files
 [*]
@@ -118,6 +118,8 @@ dotnet_style_allow_statement_immediately_after_block_experimental = true:silent
 
 # Diagnostics
 
+# CS8602: Dereference of a possibly null reference.
+dotnet_diagnostic.CS8602.severity = error
 # CS8603: Possible null reference return.
 dotnet_diagnostic.CS8603.severity = error
 dotnet_style_namespace_match_folder = true:suggestion

VSConfigFinder/FileSystem.cs

@@ -1,11 +1,13 @@
-namespace VSConfigFinder
+// <copyright file="FileSystem.cs" company="Microsoft Corporation">
+// Copyright (C) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE.txt in the project root for license information.
+// </copyright>
+
+namespace VSConfigFinder
 {
-    using System;
-    using System.ComponentModel.DataAnnotations;
-    using System.Diagnostics.CodeAnalysis;
     using System.IO;
-    using System.Text.Json;
 
+    /// <inheritdoc/>
     public class FileSystem : IFileSystem
     {
         /// <inheritdoc/>
@@ -24,5 +26,13 @@ public Stream OpenFile(string path)
 
             return File.OpenRead(path);
         }
+
+        /// <inheritdoc/>
+        public void WriteAllText(string path, string data)
+        {
+            Utilities.ValidateIsNotNullOrEmpty(path, nameof(Path));
+
+            File.WriteAllText(path, data);
+        }
     }
 }

VSConfigFinder/IFileSystem.cs

@@ -1,10 +1,42 @@
-namespace VSConfigFinder
-{
+// <copyright file="IFileSystem.cs" company="Microsoft Corporation">
+// Copyright (C) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE.txt in the project root for license information.
+// </copyright>
 
+namespace VSConfigFinder
+{
+    /// <summary>
+    /// The interface for the <see cref="FileSystem"/>.
+    /// </summary>
     public interface IFileSystem
     {
+        /// <summary>
+        /// Get files and directories within directory.
+        /// </summary>
+        /// <param name="path">directory path</param>
+        /// <param name="pattern">pattern to match for file names. To match anything and everything, specify '*'</param>
+        /// <param name="recursive">Optional: recursively search sub directories</param>
+        /// <returns>array of files within the directory</returns>
+        /// <exception cref="ArgumentException"><paramref name="path"/> is empty.</exception>
+        /// <exception cref="ArgumentNullException"><paramref name="path"/> is null.</exception>
         public string[] GetFileSystemEntries(string path, string pattern, bool recursive = false);
 
+        /// <summary>
+        /// Opens a file for reading.
+        /// </summary>
+        /// <param name="path">The path to a file to open.</param>
+        /// <returns>A stream of the opened file.</returns>
+        /// <exception cref="ArgumentException"><paramref name="path"/> is empty.</exception>
+        /// <exception cref="ArgumentNullException"><paramref name="path"/> is null.</exception>
         public Stream OpenFile(string path);
+
+        /// <summary>
+        /// Writes all text in a path.
+        /// </summary>
+        /// <param name="path">The path to a file to write.</param>
+        /// <param name="data">The string data to write.</param>
+        /// <exception cref="ArgumentException"><paramref name="path"/> is empty.</exception>
+        /// <exception cref="ArgumentNullException"><paramref name="path"/> is null.</exception>
+        public void WriteAllText(string path, string data);
     }
 }

VSConfigFinder/Program.cs

@@ -7,7 +7,6 @@ namespace VSConfigFinder
 {
     using CommandLine;
     using System.IO;
-    using System.Text.Json;
 
     /// <summary>
     /// <see cref="Program"/> class for the .vsconfig finder tool.
@@ -25,30 +24,33 @@ public static void Main(string[] args)
                 with.CaseSensitive = false;
             });
 
-            // Take in the command line arguments
             parser.ParseArguments<CommandLineOptions>(args)
                 .WithParsed(Run)
                 .WithNotParsed(HandleParseError);
         }
 
         private static void Run(CommandLineOptions options)
         {
-            // Run
-            if (options.CreateFile)
-            {
-                options.ConfigOutputPath ??= Directory.GetCurrentDirectory();
-            }
+            var fileSystem = new FileSystem();
 
-            string[] allComponents = Utilities.ReadComponents(options); 
+            ResolveCommandLineOptions(options);
 
             var finalConfig = new VSConfig()
             {
+                // This is the new final .vsconfig, so version 1.0 is used.
                 Version = new Version("1.0"),
-                Components = allComponents,
+                Components = Utilities.ReadComponents(fileSystem, options),
             };
 
-            // Output
-            Utilities.CreateOutput(finalConfig, options);
+            Utilities.CreateOutput(fileSystem, finalConfig, options);
+        }
+
+        private static void ResolveCommandLineOptions(CommandLineOptions options)
+        {
+            if (options.CreateFile)
+            {
+                options.ConfigOutputPath ??= Directory.GetCurrentDirectory();
+            }
         }
 
         private static void HandleParseError(IEnumerable<Error> errors)