Add TestDataFolderFileSystem.

src/WixBuildTools.TestSupport/RobocopyRunner.cs

@@ -0,0 +1,16 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixBuildTools.TestSupport
+{
+    public class RobocopyRunner : ExternalExecutable
+    {
+        private static readonly RobocopyRunner Instance = new RobocopyRunner();
+
+        private RobocopyRunner() : base("robocopy") { }
+
+        public static ExternalExecutableResult Execute(string args)
+        {
+            return Instance.Run(args);
+        }
+    }
+}

src/WixBuildTools.TestSupport/TestDataFolderFileSystem.cs

@@ -0,0 +1,42 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixBuildTools.TestSupport
+{
+    using System;
+
+    /// <summary>
+    /// This class builds on top of DisposableFileSystem
+    /// to make it easy to write a test that needs a whole folder of test data copied to a temp location
+    /// that will automatically be cleaned up at the end of the test.
+    /// </summary>
+    public class TestDataFolderFileSystem : IDisposable
+    {
+        private DisposableFileSystem fileSystem;
+
+        public string BaseFolder { get; private set; }
+
+        public void Dispose()
+        {
+            this.fileSystem?.Dispose();
+        }
+
+        public void Initialize(string sourceDirectoryPath)
+        {
+            if (this.fileSystem != null)
+            {
+                throw new InvalidOperationException();
+            }
+            this.fileSystem = new DisposableFileSystem();
+
+            this.BaseFolder = this.fileSystem.GetFolder();
+
+            RobocopyFolder(sourceDirectoryPath, this.BaseFolder);
+        }
+
+        private static ExternalExecutableResult RobocopyFolder(string sourceFolderPath, string destinationFolderPath)
+        {
+            var args = $"\"{sourceFolderPath}\" \"{destinationFolderPath}\" /E /R:1 /W:1";
+            return RobocopyRunner.Execute(args);
+        }
+    }
+}