Onboard to new dotnet test experience

dotnet.config

@@ -0,0 +1,2 @@
+[dotnet.test:runner]
+name= "MicrosoftTestingPlatform"

test/Utilities/Microsoft.Testing.TestInfrastructure/ProcessFactory.cs

@@ -9,7 +9,7 @@ public static IProcessHandle Start(ProcessConfiguration config, bool cleanDefaul
     {
         string fullPath = config.FileName; // Path.GetFullPath(startInfo.FileName);
         string workingDirectory = config.WorkingDirectory
-            .OrDefault(Path.GetDirectoryName(config.FileName).OrDefault(Directory.GetCurrentDirectory()));
+            .OrDefault(TempDirectory.TestSuiteDirectory);
 
         ProcessStartInfo processStartInfo = new()
         {

test/Utilities/Microsoft.Testing.TestInfrastructure/TempDirectory.cs

@@ -172,6 +172,16 @@ internal static (string BaseDirectory, string FinalDirectory) CreateUniqueDirect
         string directoryPath = System.IO.Path.Combine(TestSuiteDirectory, RandomId.Next());
         Directory.CreateDirectory(directoryPath);
 
+        // Our tests were originally wrote before the enhanced dotnet test support for MTP.
+        // So, by default we use VSTest.
+        // We can start to gradually move some of the MTP tests to the new dotnet test experience.
+        // Note that we have tests that are actually VSTest-specific.
+        string dotnetConfig = System.IO.Path.Combine(TestSuiteDirectory, "dotnet.config");
+        File.WriteAllText(dotnetConfig, """
+            [dotnet.test:runner]
+            name= "VSTest"
+            """);
+
         string directoryBuildProps = System.IO.Path.Combine(directoryPath, "Directory.Build.props");
         File.WriteAllText(directoryBuildProps, $"""
 <?xml version="1.0" encoding="utf-8"?>