add test

src/Build.UnitTests/BackEnd/DebugUtils_tests.cs

@@ -0,0 +1,38 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.IO;
+using System.Linq;
+using Microsoft.Build.Shared;
+using Shouldly;
+using Xunit;
+
+namespace Microsoft.Build.UnitTests
+{
+    public class DebugUtils_Tests
+    {
+        [Fact]
+        public void DumpExceptionToFileShouldWriteInTempPathByDefault()
+        {
+            Directory.GetFiles(Path.GetTempPath(), "MSBuild_*failure.txt").ShouldBeEmpty();
+
+            string[] exceptionFiles = null;
+
+            try
+            {
+                ExceptionHandling.DumpExceptionToFile(new Exception("hello world"));
+                exceptionFiles = Directory.GetFiles(Path.GetTempPath(), "MSBuild_*failure.txt");
+            }
+            finally
+            {
+                exceptionFiles.ShouldNotBeNull();
+                exceptionFiles.ShouldHaveSingleItem();
+
+                var exceptionFile = exceptionFiles.First();
+                File.ReadAllText(exceptionFile).ShouldContain("hello world");
+                File.Delete(exceptionFile);
+            }
+        }
+    }
+}