Rename Helper.cs into Guard.cs

Author: Evangelink

src/TestFramework/TestFramework.Extensions/PrivateObject.cs

@@ -96,7 +96,7 @@ public PrivateObject(string assemblyName, string typeName, Type[]? parameterType
     public PrivateObject(Type type, params object?[]? args)
         : this(type, null, args)
     {
-        Helper.CheckParameterNotNull(type, "type", string.Empty);
+        Guard.IsNotNull(type, "type", string.Empty);
     }
 
     /// <summary>
@@ -108,7 +108,7 @@ public PrivateObject(Type type, params object?[]? args)
     /// <param name="args">Arguments to pass to the constructor.</param>
     public PrivateObject(Type type, Type[]? parameterTypes, object?[]? args)
     {
-        Helper.CheckParameterNotNull(type, "type", string.Empty);
+        Guard.IsNotNull(type, "type", string.Empty);
         object? o;
         if (parameterTypes != null)
         {

src/TestFramework/TestFramework/Internal/Guard.cs

@@ -0,0 +1,35 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+
+namespace Microsoft.VisualStudio.TestTools.UnitTesting;
+
+/// <summary>
+/// A guard helper class to help validate preconditions.
+/// </summary>
+internal static class Guard
+{
+    internal static void IsNotNull(object? param, string parameterName, string? message)
+    {
+        if (param is not null)
+        {
+            return;
+        }
+
+        if (message is null)
+        {
+            throw new ArgumentNullException(parameterName);
+        }
+
+        throw new ArgumentNullException(parameterName, message);
+    }
+
+    internal static void IsNotNullOrEmpty(string? argument, string parameterName, string message)
+    {
+        if (StringEx.IsNullOrEmpty(argument))
+        {
+            throw new ArgumentException(message, parameterName);
+        }
+    }
+}