post migration cleanup (#4449)

* Create tests

* Basic scenario working & tested

* Feature Complete

* prevent build of intentionally broken test asset

* Update migrate command backup

* PR Feedback

* Move negative test to negative test directory

* Fix tests

* make test output directories unique

* Merge Conflict

* make backup the default behavior

* Pass2Fail

* Remove tests' PJ dependency

TestAssets/NonRestoredTestProjects/TestAppWithLibraryAndMissingP2P/TestLibrary/Helper.cs

@@ -0,0 +1,24 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+
+namespace TestLibrary
+{
+    public static class Helper
+    {
+        /// <summary>
+        /// Gets the message from the helper. This comment is here to help test XML documentation file generation, please do not remove it.
+        /// </summary>
+        /// <returns>A message</returns>
+        public static string GetMessage()
+        {
+            return "This string came from the test library!";
+        }
+
+        public static void SayHi()
+        {
+            Console.WriteLine("Hello there!");
+        }
+    }
+}

TestAssets/NonRestoredTestProjects/TestAppWithLibraryAndMissingP2P/TestLibrary/project.json

@@ -0,0 +1,22 @@
+{
+  "version": "1.0.0-*",
+  "buildOptions": {
+    "nowarn": [
+      "CS1591"
+    ],
+    "xmlDoc": true,
+    "additionalArguments": [
+      "-highentropyva+"
+    ]
+  },
+  "dependencies": {
+    "MissingP2PDependency": {
+      "target": "project",
+      "version": "1.0.0-*"
+    },
+    "NETStandard.Library": "1.6.0"
+  },
+  "frameworks": {
+    "netstandard1.5": {}
+  }
+}