[PT Run] [Folder Plugin] Environment Variables With Autocomplete (#13811)

* search environment variables folders with autocomplete

* refactoring and tests

* fix

src/modules/launcher/Plugins/Microsoft.Plugin.Folder.UnitTests/EnvironmentHelperTests.cs

@@ -0,0 +1,29 @@
+// 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 Microsoft.Plugin.Folder.Sources;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Microsoft.Plugin.Folder.UnitTests
+{
+    [TestClass]
+    public class EnvironmentHelperTests
+    {
+        [DataTestMethod]
+        [DataRow(@"%", true)]
+        [DataRow(@"%P", true)]
+        [DataRow(@"%PROGRAMDATA%", true)]
+        [DataRow(@"", false)]
+        [DataRow(@"C:\ProgramData", false)]
+
+        public void IsValidEnvironmentVariable(string search, bool expectedSuccess)
+        {
+            var helper = new EnvironmentHelper();
+
+            var result = helper.IsEnvironmentVariable(search);
+
+            Assert.AreEqual(expectedSuccess, result);
+        }
+    }
+}