[release/6.0.1xx] dotnet watch smoke test (#13392)

* add dotnet watch smoke test

src/SourceBuild/tarball/content/test/Microsoft.DotNet.SourceBuild.SmokeTests/DotNetHelper.cs

@@ -79,14 +79,25 @@ internal class DotNetHelper
         }
     }
 
-    public void ExecuteCmd(string args, string? workingDirectory = null)
+    public void ExecuteCmd(string args, string? workingDirectory = null, Action<Process>? additionalProcessConfigCallback = null, int expectedExitCode = 0, int millisecondTimeout = -1)
     {
+        Action<Process, string?> configureProcess = (Process process, string? workingDirectory) => {
+            ConfigureProcess(process, workingDirectory);
+
+            if (additionalProcessConfigCallback != null)
+            {
+                additionalProcessConfigCallback(process);
+            }
+        };
+
         (Process Process, string StdOut, string StdErr) executeResult = ExecuteHelper.ExecuteProcess(
             DotNetPath,
             args,
             OutputHelper,
-            configure: (process) => ConfigureProcess(process, workingDirectory));
+            configure: (process) => configureProcess(process, workingDirectory),
-        ExecuteHelper.ValidateExitCode(executeResult);
+            millisecondTimeout: millisecondTimeout);
+        
+        ExecuteHelper.ValidateExitCode(executeResult, expectedExitCode);
     }
 
     public static void ConfigureProcess(Process process, string? workingDirectory, bool setPath = false)
@@ -170,18 +181,14 @@ internal class DotNetHelper
 
     public void ExecuteRunWeb(string projectName)
     {
-        (Process Process, string StdOut, string StdErr) executeResult = ExecuteHelper.ExecuteProcess(
+        ExecuteCmd(
-            DotNetPath,
             $"run {GetBinLogOption(projectName, "run")}",
-            OutputHelper,
+            GetProjectDirectory(projectName),
-            configure: configureProcess,
+            additionalProcessConfigCallback: processConfigCallback,
             millisecondTimeout: 30000);
-        ExecuteHelper.ValidateExitCode(executeResult);
 
-        void configureProcess(Process process)
+        void processConfigCallback(Process process)
         {
-            ConfigureProcess(process, GetProjectDirectory(projectName));
-
             process.OutputDataReceived += new DataReceivedEventHandler((sender, e) =>
             {
                 if (e.Data?.Contains("Application started. Press Ctrl+C to shut down.") ?? false)

src/SourceBuild/tarball/content/test/Microsoft.DotNet.SourceBuild.SmokeTests/DotNetWatchTests.cs

@@ -0,0 +1,60 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using System.IO;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.DotNet.SourceBuild.SmokeTests;
+
+public class DotNetWatchTests : SmokeTests
+{
+    public DotNetWatchTests(ITestOutputHelper outputHelper) : base(outputHelper) { }
+
+    [Fact]
+    public void WatchTests()
+    {
+        string projectDirectory = DotNetHelper.ExecuteNew(DotNetTemplate.Console.GetName(), nameof(DotNetWatchTests));
+        bool outputChanged = false;
+
+        // We expect an exit code of 143 (128 + 15, i.e. SIGTERM) because we are killing the process manually
+        DotNetHelper.ExecuteCmd(
+            "watch run",
+            workingDirectory: projectDirectory,
+            additionalProcessConfigCallback: processConfigCallback,
+            expectedExitCode: 143,
+            millisecondTimeout: 30000);
+
+        Assert.True(outputChanged);
+
+        void processConfigCallback(Process process)
+        {
+            const string waitingString = "Waiting for a file to change before restarting dotnet...";
+            const string expectedString = "Hello from dotnet watch!";
+
+            bool fileChanged = false;
+
+            process.OutputDataReceived += new DataReceivedEventHandler((sender, e) =>
+            {
+                if (e.Data?.Contains(waitingString) ?? false)
+                {
+                    if (!fileChanged) {
+                        OutputHelper.WriteLine("Program started, changing file on disk to trigger restart...");
+                        File.WriteAllText(
+                            Path.Combine(projectDirectory, "Program.cs"),
+                            File.ReadAllText(Path.Combine(projectDirectory, "Program.cs")).Replace("Hello, World!", expectedString));
+                        fileChanged = true;
+                    }
+                }
+                else if (e.Data?.Contains(expectedString) ?? false)
+                {
+                    outputChanged = true;
+                    OutputHelper.WriteLine("Successfully re-ran program after code change.");
+                    ExecuteHelper.ExecuteProcessValidateExitCode("kill", $"-s TERM {process.Id}", OutputHelper);
+                }
+            });
+        }
+    }
+}

src/SourceBuild/tarball/content/test/Microsoft.DotNet.SourceBuild.SmokeTests/ExecuteHelper.cs

@@ -84,9 +84,9 @@ internal static class ExecuteHelper
         return result.StdOut;
     }
 
-    public static void ValidateExitCode((Process Process, string StdOut, string StdErr) result)
+    public static void ValidateExitCode((Process Process, string StdOut, string StdErr) result, int expectedExitCode = 0)
     {
-        if (result.Process.ExitCode != 0)
+        if (result.Process.ExitCode != expectedExitCode)
         {
             ProcessStartInfo startInfo = result.Process.StartInfo;
             string msg = $"Failed to execute {startInfo.FileName} {startInfo.Arguments}" +