[Tests] Fixes random test failures

- The Stride.GameStudio.Tests must not run in parallel
- The Stride.Core.Assets.Tests could fail if the hard disk wouldn't react fast enough

sources/assets/Stride.Core.Assets.Tests/TestFileVersionManager.cs

@@ -7,6 +7,7 @@
 using Xunit;
 using Stride.Core.IO;
 using Stride.Core.Storage;
+using System.Threading.Tasks;
 
 namespace Stride.Core.Assets.Tests
 {
@@ -43,7 +44,7 @@ public void Test()
 
 
         [Fact]
-        public void TestAsync()
+        public async Task TestAsync()
         {
             var files = new List<UFile>();
             for (int i = 0; i < 10; i++)
@@ -54,8 +55,14 @@ public void TestAsync()
             }
 
             var ids = new List<Tuple<UFile, ObjectId>>();
-            FileVersionManager.Instance.ComputeFileHashAsync(files, (file, id) => ids.Add(new Tuple<UFile, ObjectId>(file, id)));
-            Thread.Sleep(200);
+            var tcs = new TaskCompletionSource();
+            FileVersionManager.Instance.ComputeFileHashAsync(files, (file, id) =>
+            {
+                ids.Add(new Tuple<UFile, ObjectId>(file, id));
+                if (ids.Count == files.Count)
+                    tcs.SetResult();
+            });
+            await tcs.Task.WaitAsync(TimeSpan.FromSeconds(5));
 
             Assert.Equal(files.Count, ids.Count);
 

sources/editor/Stride.GameStudio.Tests/XunitAttributes.cs

@@ -0,0 +1,6 @@
+// Copyright (c) .NET Foundation and Contributors (https://dotnetfoundation.org/ & https://stride3d.net) and Silicon Studio Corp. (https://www.siliconstudio.co.jp)
+// Distributed under the MIT license. See the LICENSE.md file in the project root for more information.
+
+using Xunit;
+
+[assembly: CollectionBehavior(DisableTestParallelization = true)]