Use rich mock to test InstallCommand (#8402)

To ensure the mock has the same behavior the component has, run mock under the same tests the adapter has.
It is a common problem that moq has -- "everything is mocked out, you are not test anything"

test/Microsoft.DotNet.Tools.Tests.ComponentMocks/ShellShimMakerMock.cs

@@ -0,0 +1,58 @@
+// 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;
+using System.IO;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ShellShim;
+using Microsoft.Extensions.EnvironmentAbstractions;
+using Newtonsoft.Json;
+
+namespace Microsoft.DotNet.Tools.Tests.ComponentMocks
+{
+    internal class ShellShimMakerMock : IShellShimMaker
+    {
+        private static IFileSystem _fileSystem;
+        private readonly string _pathToPlaceShim;
+
+        public ShellShimMakerMock(string pathToPlaceShim, IFileSystem fileSystem = null)
+        {
+            _pathToPlaceShim =
+                pathToPlaceShim ?? throw new ArgumentNullException(nameof(pathToPlaceShim));
+
+            _fileSystem = fileSystem ?? new FileSystemWrapper();
+        }
+
+        public void CreateShim(string packageExecutablePath, string shellCommandName)
+        {
+            var packageExecutable = new FilePath(packageExecutablePath);
+
+
+            var fakeshim = new FakeShim
+            {
+                Runner = "dotnet",
+                ExecutablePath = packageExecutable.Value
+            };
+            var script = JsonConvert.SerializeObject(fakeshim);
+
+            FilePath scriptPath = new FilePath(Path.Combine(_pathToPlaceShim, shellCommandName));
+            _fileSystem.File.WriteAllText(scriptPath.Value, script);
+        }
+
+        public void EnsureCommandNameUniqueness(string shellCommandName)
+        {
+            if (_fileSystem.File.Exists(Path.Combine(_pathToPlaceShim, shellCommandName)))
+            {
+                throw new GracefulException(
+                    string.Format(CommonLocalizableStrings.FailInstallToolSameName,
+                        shellCommandName));
+            }
+        }
+
+        public class FakeShim
+        {
+            public string Runner { get; set; }
+            public string ExecutablePath { get; set; }
+        }
+    }
+}