unit tests for dotnet-cache invocation, some cleanup

src/dotnet/commands/dotnet-cache/Program.cs

@@ -5,12 +5,14 @@ using System.Collections.Generic;
 using Microsoft.DotNet.Cli.CommandLine;
 using Microsoft.DotNet.Cli.Utils;
 using Microsoft.DotNet.Tools.MSBuild;
+using Microsoft.DotNet.Cli;
+using System.Diagnostics;
 
 namespace Microsoft.DotNet.Tools.Cache
 {
     public partial class CacheCommand
     {
-        public static int Run(string[] args)
+        public static CacheCommand FromArgs(string[] args, string msbuildPath = null)
         {
             DebugHelper.HandleDebugSwitch(ref args);
 
@@ -56,10 +58,11 @@ namespace Microsoft.DotNet.Tools.Cache
 
             CommandOption verbosityOption = MSBuildForwardingApp.AddVerbosityOption(app);
 
+            var cache = new CacheCommand(msbuildPath);
+            bool commandExecuted = false;
             app.OnExecute(() =>
             {
-                var cache = new CacheCommand();
-
+                commandExecuted = true;
                 cache.Framework = frameworkOption.Value();
                 cache.Runtime = runtimeOption.Value();
                 cache.OutputPath = outputOption.Value();
@@ -71,10 +74,43 @@ namespace Microsoft.DotNet.Tools.Cache
                 cache.ExtraMSBuildArguments = app.RemainingArguments;
                 cache.ProjectArgument = projectArgument.Value();
                
-                return cache.Execute();
+                return 0;
             });
 
-            return app.Execute(args);
+            int exitCode = app.Execute(args);
+            if (!commandExecuted)
+            {
+                throw new CommandCreationException(exitCode);
+            }
+
+            return cache;
+        }
+
+        public static int Run(string[] args)
+        {
+            DebugHelper.HandleDebugSwitch(ref args);
+
+            CacheCommand cmd;
+            try
+            {
+                cmd = FromArgs(args);
+            }
+            catch (CommandCreationException e)
+            {
+                return e.ExitCode;
+            }
+
+            return cmd.Execute();
+        }
+
+        public ProcessStartInfo GetProcessStartInfo()
+        {
+            return CreateForwardingApp(_msbuildPath).GetProcessStartInfo();
+        }
+
+        public int Execute()
+        {
+            return GetProcessStartInfo().Execute();
         }
     }
 }