Fix race condition in test code waiting for dotnet-watch to restart

Author: Nate McMaster

src/dotnet-watch/Internal/ProcessRunner.cs

@@ -105,9 +105,23 @@ public ProcessState(Process process)
             {
                 _process = process;
                 _process.Exited += OnExited;
+                Task = _tcs.Task.ContinueWith(_ =>
+                {
+                    // We need to use two WaitForExit calls to ensure that all of the output/events are processed. Previously
+                    // this code used Process.Exited, which could result in us missing some output due to the ordering of
+                    // events.
+                    //
+                    // See the remarks here: https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.process.waitforexit#System_Diagnostics_Process_WaitForExit_System_Int32_
+                    if (!process.WaitForExit(Int32.MaxValue))
+                    {
+                        throw new TimeoutException();
+                    }
+
+                    process.WaitForExit();
+                });
             }
 
-            public Task Task => _tcs.Task;
+            public Task Task { get; }
 
             public void TryKill()
             {

test/dotnet-watch.FunctionalTests/AwaitableProcess.cs

@@ -116,6 +116,8 @@ private void OnData(object sender, DataReceivedEventArgs args)
 
         private void OnExit(object sender, EventArgs args)
         {
+            // Wait to ensure the process has exited and all output consumed
+            _process.WaitForExit();
             _source.Complete();
         }
 

test/dotnet-watch.FunctionalTests/NoDepsAppTests.cs

@@ -41,7 +41,7 @@ public async Task RestartProcessOnFileChange()
             Assert.Throws<ArgumentException>(() => Process.GetProcessById(pid));
         }
 
-        [Fact(Skip="https://github.com/aspnet/DotNetTools/issues/407")]
+        [Fact]
         public async Task RestartProcessThatTerminatesAfterFileChange()
         {
             await _app.StartWatcherAsync();

test/dotnet-watch.FunctionalTests/Scenario/WatchableApp.cs

@@ -18,6 +18,7 @@ public class WatchableApp : IDisposable
 
         private const string StartedMessage = "Started";
         private const string ExitingMessage = "Exiting";
+        private const string WatchExitedMessage = "watch : Exited";
 
         private readonly ITestOutputHelper _logger;
         private string _appName;
@@ -42,8 +43,11 @@ public WatchableApp(string appName, ITestOutputHelper logger)
         public Task HasRestarted()
             => Process.GetOutputLineAsync(StartedMessage, DefaultMessageTimeOut);
 
-        public Task HasExited()
-            => Process.GetOutputLineAsync(ExitingMessage, DefaultMessageTimeOut);
+        public async Task HasExited()
+        {
+            await Process.GetOutputLineAsync(ExitingMessage, DefaultMessageTimeOut);
+            await Process.GetOutputLineAsync(WatchExitedMessage, DefaultMessageTimeOut);
+        }
 
         public bool UsePollingWatcher { get; set; }