Reduce flakiness in tests caused by the OS re-using the PID on test processes (#512)

We were using PID to assert that dotnet-watch had restarted processes. The OS does not guaranteed the uniqueness of PID, so I've changed tests to use PID + process start time to distinguish between processes.

test/dotnet-watch.FunctionalTests/NoDepsAppTests.cs

@@ -27,7 +27,7 @@ namespace Microsoft.DotNet.Watcher.Tools.FunctionalTests
         public async Task RestartProcessOnFileChange()
         {
             await _app.StartWatcherAsync(new[] { "--no-exit" });
-            var pid = await _app.GetProcessId();
+            var processIdentifier = await _app.GetProcessIdentifier();
 
             // Then wait for it to restart when we change a file
             var fileToChange = Path.Combine(_app.SourceDirectory, "Program.cs");
@@ -37,15 +37,15 @@ namespace Microsoft.DotNet.Watcher.Tools.FunctionalTests
             await _app.HasRestarted();
             Assert.DoesNotContain(_app.Process.Output, l => l.StartsWith("Exited with error code"));
 
-            var pid2 = await _app.GetProcessId();
+            var processIdentifier2 = await _app.GetProcessIdentifier();
-            Assert.NotEqual(pid, pid2);
+            Assert.NotEqual(processIdentifier, processIdentifier2);
         }
 
         [Fact]
         public async Task RestartProcessThatTerminatesAfterFileChange()
         {
             await _app.StartWatcherAsync();
-            var pid = await _app.GetProcessId();
+            var processIdentifier = await _app.GetProcessIdentifier();
             await _app.HasExited(); // process should exit after run
             await _app.IsWaitingForFileChange();
 
@@ -63,8 +63,8 @@ namespace Microsoft.DotNet.Watcher.Tools.FunctionalTests
                 await _app.HasRestarted();
             }
 
-            var pid2 = await _app.GetProcessId();
+            var processIdentifier2 = await _app.GetProcessIdentifier();
-            Assert.NotEqual(pid, pid2);
+            Assert.NotEqual(processIdentifier, processIdentifier2);
             await _app.HasExited(); // process should exit after run
         }
 

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

@@ -57,11 +57,12 @@ namespace Microsoft.DotNet.Watcher.Tools.FunctionalTests
 
         public bool UsePollingWatcher { get; set; }
 
-        public async Task<int> GetProcessId()
+        public async Task<string> GetProcessIdentifier()
         {
-            var line = await Process.GetOutputLineStartsWithAsync("PID =", DefaultMessageTimeOut);
+            // Process ID is insufficient because PID's may be reused. Process identifier also includes other info to distinguish
-            var pid = line.Split('=').Last();
+            // between different process instances.
-            return int.Parse(pid);
+            var line = await Process.GetOutputLineStartsWithAsync("Process identifier =", DefaultMessageTimeOut);
+            return line.Split('=').Last();
         }
 
         public async Task PrepareAsync()

test/dotnet-watch.FunctionalTests/TestProjects/AppWithDeps/Program.cs

@@ -14,7 +14,8 @@ namespace ConsoleApplication
         public static void Main(string[] args)
         {
             Console.WriteLine("Started");
-            Console.WriteLine($"PID = " + Process.GetCurrentProcess().Id);
+            // Process ID is insufficient because PID's may be reused.
+            Console.WriteLine($"Process identifier = {Process.GetCurrentProcess().Id}, {Process.GetCurrentProcess().StartTime:hh:mm:ss.FF}");
             Thread.Sleep(Timeout.Infinite);
         }
     }

test/dotnet-watch.FunctionalTests/TestProjects/GlobbingApp/Program.cs

@@ -14,7 +14,8 @@ namespace ConsoleApplication
         public static void Main(string[] args)
         {
             Console.WriteLine("Started");
-            Console.WriteLine("PID = " + Process.GetCurrentProcess().Id);
+            // Process ID is insufficient because PID's may be reused.
+            Console.WriteLine($"Process identifier = {Process.GetCurrentProcess().Id}, {Process.GetCurrentProcess().StartTime:hh:mm:ss.FF}");
             Console.WriteLine("Defined types = " + typeof(Program).GetTypeInfo().Assembly.DefinedTypes.Count());
             Thread.Sleep(Timeout.Infinite);
         }

test/dotnet-watch.FunctionalTests/TestProjects/KitchenSink/Program.cs

@@ -11,7 +11,8 @@ namespace KitchenSink
         static void Main(string[] args)
         {
             Console.WriteLine("Started");
-            Console.WriteLine("PID = " + Process.GetCurrentProcess().Id);
+            // Process ID is insufficient because PID's may be reused.
+            Console.WriteLine($"Process identifier = {Process.GetCurrentProcess().Id}, {Process.GetCurrentProcess().StartTime:hh:mm:ss.FF}");
             Console.WriteLine("DOTNET_WATCH = " + Environment.GetEnvironmentVariable("DOTNET_WATCH"));
             Console.WriteLine("DOTNET_WATCH_ITERATION = " + Environment.GetEnvironmentVariable("DOTNET_WATCH_ITERATION"));
         }

test/dotnet-watch.FunctionalTests/TestProjects/NoDepsApp/Program.cs

@@ -12,7 +12,8 @@ namespace ConsoleApplication
         public static void Main(string[] args)
         {
             Console.WriteLine("Started");
-            Console.WriteLine($"PID = " + Process.GetCurrentProcess().Id);
+            // Process ID is insufficient because PID's may be reused.
+            Console.WriteLine($"Process identifier = {Process.GetCurrentProcess().Id}, {Process.GetCurrentProcess().StartTime:hh:mm:ss.FF}");
             if (args.Length > 0 && args[0] == "--no-exit")
             {
                 Thread.Sleep(Timeout.Infinite);