Add kestrel tests.

Tests will 'build', 'run', 'publish' and 'execute' a Kestrel Hello World server as a PortableFatApp and as a Standalone app.

test/Microsoft.DotNet.Tools.Tests.Utilities/ProcessExtensions.cs

@@ -0,0 +1,110 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Runtime.InteropServices;
+
+namespace Microsoft.DotNet.Tools.Test.Utilities
+{
+    internal static class ProcessExtensions
+    {
+        private static readonly bool _isWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+        private static readonly TimeSpan _defaultTimeout = TimeSpan.FromSeconds(30);
+
+        public static void KillTree(this Process process)
+        {
+            process.KillTree(_defaultTimeout);
+        }
+
+        public static void KillTree(this Process process, TimeSpan timeout)
+        {
+            string stdout;
+            if (_isWindows)
+            {
+                RunProcessAndWaitForExit(
+                    "taskkill",
+                    $"/T /F /PID {process.Id}",
+                    timeout,
+                    out stdout);
+            }
+            else
+            {
+                var children = new HashSet<int>();
+                GetAllChildIdsUnix(process.Id, children, timeout);
+                foreach (var childId in children)
+                {
+                    KillProcessUnix(childId, timeout);
+                }
+                KillProcessUnix(process.Id, timeout);
+            }
+        }
+
+        private static void GetAllChildIdsUnix(int parentId, ISet<int> children, TimeSpan timeout)
+        {
+            string stdout;
+            var exitCode = RunProcessAndWaitForExit(
+                "pgrep",
+                $"-P {parentId}",
+                timeout,
+                out stdout);
+
+            if (exitCode == 0 && !string.IsNullOrEmpty(stdout))
+            {
+                using (var reader = new StringReader(stdout))
+                {
+                    while (true)
+                    {
+                        var text = reader.ReadLine();
+                        if (text == null)
+                        {
+                            return;
+                        }
+
+                        int id;
+                        if (int.TryParse(text, out id))
+                        {
+                            children.Add(id);
+                            // Recursively get the children
+                            GetAllChildIdsUnix(id, children, timeout);
+                        }
+                    }
+                }
+            }
+        }
+
+        private static void KillProcessUnix(int processId, TimeSpan timeout)
+        {
+            string stdout;
+            RunProcessAndWaitForExit(
+                "kill",
+                $"-TERM {processId}",
+                timeout,
+                out stdout);
+        }
+
+        private static int RunProcessAndWaitForExit(string fileName, string arguments, TimeSpan timeout, out string stdout)
+        {
+            var startInfo = new ProcessStartInfo
+            {
+                FileName = fileName,
+                Arguments = arguments,
+                RedirectStandardOutput = true,
+                UseShellExecute = false
+            };
+
+            var process = Process.Start(startInfo);
+
+            stdout = null;
+            if (process.WaitForExit((int)timeout.TotalMilliseconds))
+            {
+                stdout = process.StandardOutput.ReadToEnd();
+            }
+            else
+            {
+                process.Kill();
+            }
+
+            return process.ExitCode;
+        }
+    }
+}