preview of single unit test for dotnet build

src/dotnet/ForwardingApp.cs

@@ -67,6 +67,11 @@ namespace Microsoft.DotNet.Cli
         }
 
         public int Execute()
+        {
+            return GetProcessStartInfo().Execute();
+        }
+
+        public ProcessStartInfo GetProcessStartInfo()
         {
             var processInfo = new ProcessStartInfo
             {
@@ -83,15 +88,7 @@ namespace Microsoft.DotNet.Cli
                 }
             }
 
-            var process = new Process
+            return processInfo;
-            {
-                StartInfo = processInfo
-            };
-
-            process.Start();
-            process.WaitForExit();
-
-            return process.ExitCode;
         }
 
         public ForwardingApp WithEnvironmentVariable(string name, string value)

src/dotnet/ProcessStartInfoExtensions.cs

@@ -0,0 +1,20 @@
+using System.Diagnostics;
+
+namespace Microsoft.DotNet.Cli
+{
+    internal static class ProcessStartInfoExtensions
+    {
+        public static int Execute(this ProcessStartInfo startInfo)
+        {
+            var process = new Process
+            {
+                StartInfo = startInfo
+            };
+
+            process.Start();
+            process.WaitForExit();
+
+            return process.ExitCode;
+        }
+    }
+}

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

@@ -5,21 +5,33 @@ using System.Collections.Generic;
 using Microsoft.DotNet.Cli.CommandLine;
 using Microsoft.DotNet.Cli.Utils;
 using Microsoft.DotNet.Tools.MSBuild;
+using System.Diagnostics;
+using System;
+using Microsoft.DotNet.Cli;
 
 namespace Microsoft.DotNet.Tools.Build
 {
     public class BuildCommand
     {
-        public static int Run(string[] args)
+        private MSBuildForwardingApp _forwardingApp;
+
+        private BuildCommand() { }
+
+        public BuildCommand(IEnumerable<string> msbuildArgs)
         {
-            DebugHelper.HandleDebugSwitch(ref args);
+            _forwardingApp = new MSBuildForwardingApp(msbuildArgs);
+        }
+
+        public static BuildCommand FromArgs(params string[] args)
+        {
+            var ret = new BuildCommand();
 
             CommandLineApplication app = new CommandLineApplication(throwOnUnexpectedArg: false);
             app.Name = "dotnet build";
             app.FullName = LocalizableStrings.AppFullName;
             app.Description = LocalizableStrings.AppDescription;
             app.ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText;
-            app.HandleRemainingArguments = true;            
+            app.HandleRemainingArguments = true;
             app.HelpOption("-h|--help");
 
             CommandArgument projectArgument = app.Argument($"<{LocalizableStrings.ProjectArgumentValueName}>", LocalizableStrings.ProjectArgumentDescription);
@@ -36,8 +48,10 @@ namespace Microsoft.DotNet.Tools.Build
             CommandOption noDependenciesOption = app.Option("--no-dependencies", LocalizableStrings.NoDependenciesOptionDescription, CommandOptionType.NoValue);
             CommandOption verbosityOption = MSBuildForwardingApp.AddVerbosityOption(app);
 
+            bool codeExecuted = false;
             app.OnExecute(() =>
             {
+                codeExecuted = true;
                 List<string> msbuildArgs = new List<string>();
 
                 if (!string.IsNullOrEmpty(projectArgument.Value))
@@ -93,10 +107,55 @@ namespace Microsoft.DotNet.Tools.Build
 
                 msbuildArgs.AddRange(app.RemainingArguments);
 
-                return new MSBuildForwardingApp(msbuildArgs).Execute();
+                ret._forwardingApp = new MSBuildForwardingApp(msbuildArgs);
+
+                return 0;
             });
 
-            return app.Execute(args);
+            int exitCode = app.Execute();
+            if (!codeExecuted)
+            {
+                throw new NonZeroExitCodeException(exitCode);
+            }
+
+            return ret;
+        }
+
+        public static int Run(string[] args)
+        {
+            DebugHelper.HandleDebugSwitch(ref args);
+
+            BuildCommand cmd;
+            try
+            {
+                cmd = FromArgs(args);
+            }
+            catch (NonZeroExitCodeException e)
+            {
+                return e.ExitCode;
+            }
+
+            return cmd.Execute();
+        }
+
+        public ProcessStartInfo GetProcessStartInfo()
+        {
+            return _forwardingApp.GetProcessStartInfo();
+        }
+
+        public int Execute()
+        {
+            return GetProcessStartInfo().Execute();
+        }
+
+        private class NonZeroExitCodeException : Exception
+        {
+            public int ExitCode { get; private set; }
+
+            public NonZeroExitCodeException(int exitCode)
+            {
+                ExitCode = exitCode;
+            }
         }
     }
 }

src/dotnet/commands/dotnet-msbuild/MSBuildForwardingApp.cs

@@ -9,6 +9,7 @@ using System.Reflection;
 using System.Runtime.InteropServices;
 using Microsoft.DotNet.Cli;
 using Microsoft.DotNet.Cli.CommandLine;
+using System.Diagnostics;
 
 namespace Microsoft.DotNet.Tools.MSBuild
 {
@@ -59,18 +60,16 @@ namespace Microsoft.DotNet.Tools.MSBuild
                 environmentVariables: _msbuildRequiredEnvironmentVariables);
         }
 
+        public ProcessStartInfo GetProcessStartInfo()
+        {
+            return _forwardingApp
+                .WithEnvironmentVariable(TelemetrySessionIdEnvironmentVariableName, Telemetry.CurrentSessionId)
+                .GetProcessStartInfo();
+        }
+
         public int Execute()
         {
-            try
+            return GetProcessStartInfo().Execute();
-            {
-                Environment.SetEnvironmentVariable(TelemetrySessionIdEnvironmentVariableName, Telemetry.CurrentSessionId);
-
-                return _forwardingApp.Execute();
-            }
-            finally
-            {
-                Environment.SetEnvironmentVariable(TelemetrySessionIdEnvironmentVariableName, null);
-            }
         }
 
         internal static CommandOption AddVerbosityOption(CommandLineApplication app)

test/dotnet-msbuild.Tests/GivenDotnetBuildInvocation.cs

@@ -0,0 +1,21 @@
+using Microsoft.DotNet.Tools.Build;
+using System;
+using System.Collections.Generic;
+using System.Text;
+using FluentAssertions;
+using Xunit;
+using System.IO;
+
+namespace Microsoft.DotNet.Cli.MSBuild.Tests
+{
+    public class GivenDotnetBuildInvocation
+    {
+        [Fact]
+        public void WhenNoArgsArePassedThenMsbuildInvocationIsCorrect()
+        {
+            var msbuildPath = Path.Combine(Directory.GetCurrentDirectory(), "MSBuild.dll");
+            BuildCommand.FromArgs()
+                .GetProcessStartInfo().Arguments.Should().Be($@"exec {msbuildPath} /m /v:m /t:Build /clp:Summary");
+        }
+    }
+}