[PTRun][Folder]Expand environment variables(#19791)

* Fix for issue 19428
Expand the environmental variables before path combine

* Adding unit test

src/modules/launcher/Plugins/Microsoft.Plugin.Folder.UnitTests/Sources/Path/FolderHelperTests.cs

@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.IO;
+using Microsoft.Plugin.Folder.Sources;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Microsoft.Plugin.Folder.Sources.Tests
+{
+    [TestClass]
+    public class FolderHelperTests
+    {
+        [DataTestMethod]
+        [DataRow(@"%SYSTEMDRIVE%", true)]
+        [DataRow(@"%O%S", false)]
+        [DataRow(@"abcd", false)]
+        [DataRow(@"%ProgramData%", true)]
+        [DataRow(@"%USERPROFILE%", true)]
+        [DataRow(@"powertoys", false)]
+
+        // can't test %HOMEPATH% on CI, so using \User as ExpandEnvironmentVariables was moved up
+        [DataRow(@"\Users", true)]
+        [DataRow(@"Users", false)]
+        public void ExpandsToRootedPath(string query, bool expected)
+        {
+            var expandedQuery = FolderHelper.Expand(query);
+            var result = Path.IsPathRooted(expandedQuery);
+            Assert.AreEqual(expected, result);
+        }
+    }
+}