Fix race in incremental build tests

Mono.TextTemplating.Build.Tests/MSBuildExecutionTests.cs

@@ -1,10 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
-using System;
-using System.IO;
 using System.Linq;
-
 using Xunit;
 
 namespace Mono.TextTemplating.Tests
@@ -154,23 +151,22 @@ void AssertNoopBuild ()
 			AssertNoopBuild ();
 
 			// check touching a template causes rebuild of that file only
-			File.SetLastWriteTime (fooTemplate, DateTime.Now);
+			WriteTimeTracker.SetWriteTimeNewerThan (barWriteTime, barTemplate);
 			ExecuteAndValidate ();
-			fooWriteTime.AssertChanged ();
-			barWriteTime.AssertSame ();
+			fooWriteTime.AssertSame ();
+			barWriteTime.AssertChanged ();
 
 			AssertNoopBuild ();
 
 			// check touching the include causes rebuild of the file that uses it
-			File.SetLastWriteTime (includeFile, DateTime.Now);
+			WriteTimeTracker.SetWriteTimeNewerThan (fooWriteTime, includeFile);
 			ExecuteAndValidate ();
 			fooWriteTime.AssertChanged ();
 			barWriteTime.AssertSame ();
 
 			AssertNoopBuild ();
 
 			// check changing a parameter causes rebuild of both files
-			File.SetLastWriteTime (includeFile, DateTime.Now);
 			project.Project.GetItems ("T4Argument").Single (i => i.UnevaluatedInclude == "Year").SetMetadataValue ("Value", "2021");
 			ExecuteAndValidate ();
 			fooGenerated.AssertTextStartsWith ("Helper says Hello 2021!");

Mono.TextTemplating.Build.Tests/Mono.TextTemplating.Build.Tests.csproj

@@ -34,6 +34,7 @@
     <None Include="TestCases\**\*.*" />
     <Compile Include="..\Mono.TextTemplating.Tests\Platform.cs" />
     <Compile Include="..\Mono.TextTemplating.Tests\TestDataPath.cs" />
+    <Compile Include="..\Mono.TextTemplating.Tests\WriteTimeTracker.cs" />
   </ItemGroup>
 
 </Project>

Mono.TextTemplating.Tests/TestDataPath.cs

@@ -147,15 +147,6 @@ public DateTime AssertWriteTimeNewerThan (DateTime previousWriteTime)
 	}
 }
 
-sealed class WriteTimeTracker
-{
-	readonly TestDataPath file;
-	DateTime lastWriteTime;
-	public WriteTimeTracker (TestDataPath file) => lastWriteTime = (this.file = file).GetLastWriteTime ();
-	public void AssertChanged () => lastWriteTime = file.AssertWriteTimeNewerThan (lastWriteTime);
-	public void AssertSame () => file.AssertWriteTimeEquals (lastWriteTime);
-}
-
 static class StringNormalizationExtensions
 {
 	public static string NormalizeNewlines (this string s, string newLine = "\n") => s.Replace ("\r\n", "\n").Replace ("\n", newLine);

Mono.TextTemplating.Tests/WriteTimeTracker.cs

@@ -0,0 +1,65 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading;
+
+namespace Mono.TextTemplating.Tests;
+
+sealed class WriteTimeTracker
+{
+	readonly TestDataPath file;
+	DateTime lastWriteTime;
+	public WriteTimeTracker (TestDataPath file) => lastWriteTime = (this.file = file).GetLastWriteTime ();
+	public void AssertChanged () => lastWriteTime = file.AssertWriteTimeNewerThan (lastWriteTime);
+	public void AssertSame () => file.AssertWriteTimeEquals (lastWriteTime);
+
+	public DateTime WaitUntilLaterNow () => LaterNowThan (lastWriteTime);
+
+	static DateTime GetNewestWriteTime (IEnumerable<WriteTimeTracker> trackers)
+	{
+		DateTime newest = DateTime.MinValue;
+		foreach (var tracker in trackers) {
+			if (newest < tracker.lastWriteTime) {
+				newest = tracker.lastWriteTime;
+			}
+		}
+		return newest;
+	}
+
+	public static void SetWriteTimeNewerThan (IEnumerable<WriteTimeTracker> trackers, string filePath)
+		=> SetWriteTimeNewerThan (GetNewestWriteTime (trackers), filePath);
+
+	public static void SetWriteTimeNewerThan (WriteTimeTracker tracker, string filePath)
+		=> SetWriteTimeNewerThan (tracker.lastWriteTime, filePath);
+
+	public static void SetWriteTimeNewerThan (IEnumerable<WriteTimeTracker> trackers, params string[] filePaths)
+		=> SetWriteTimeNewerThan (GetNewestWriteTime (trackers), filePaths);
+
+	public static void SetWriteTimeNewerThan (WriteTimeTracker tracker, params string[] filePaths)
+		=> SetWriteTimeNewerThan (tracker.lastWriteTime, filePaths);
+
+	/// <summary>
+	/// Waits until `DateTime.Now` is newer than `time`, then return this newer value.
+	/// </summary>
+	static DateTime LaterNowThan (DateTime time)
+	{
+		DateTime now;
+		while ((now = DateTime.Now) <= time) {
+			Thread.Sleep (10);
+		}
+		return now;
+	}
+
+	static void SetWriteTimeNewerThan (DateTime time, string filePath) => File.SetLastWriteTime (filePath, LaterNowThan (time));
+
+	static void SetWriteTimeNewerThan (DateTime time, params string[] filePaths)
+	{
+		var now = LaterNowThan (time);
+		foreach (var file in filePaths) {
+			File.SetLastWriteTime (file, now);
+		}
+	}
+}