Targeting .NET 6 seems to trigger exception in some odd circumstances

[CptWesley]

Previous project setup where -> denotes a dependency:

project A;
project A.SourceGenerator;
project A.Tests;

project A -> project A.SourceGenerator;
project A.Tests -> TUnit;
project A.Tests -> A;

The tests worked perfectly fine when A.Tests targeted both net6.0 and net9.0.

Now I introduced another source generator:

project A;
project A.SourceGenerator;
project A.AnotherSourceGenerator;
project A.Tests;

project A -> project A.SourceGenerator;
project A -> project A.AnotherSourceGenerator;
project A.Tests -> TUnit;
project A.Tests -> A;

The new source generator does not generate any code that is hit by any tests in A.Tests and works fine when targeting net9.0 (as one would expect, since from the A.Tests perspective, nothing really changed), but when targeting net6.0 we suddenly run into the following exception:

Unhandled exception. System.MissingMethodException: Method not found: 'Void Microsoft.Testing.Platform.Extensions.Messages.TestNode.set_DisplayName(System.String)'.
   at TUnit.Engine.Framework.TUnitTestFramework.ExecuteRequestAsync(ExecuteRequestContext context)
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start[TStateMachine](TStateMachine& stateMachine)
   at TUnit.Engine.Framework.TUnitTestFramework.ExecuteRequestAsync(ExecuteRequestContext context)
   at Microsoft.Testing.Platform.Requests.TestHostTestFrameworkInvoker.ExecuteRequestAsync(ITestFramework testFramework, TestExecutionRequest request, IMessageBus messageBus, CancellationToken cancellationToken) in /_/src/Platform/Microsoft.Testing.Platform/Requests/TestHostTestFrameworkInvoker.cs:line 73
   at Microsoft.Testing.Platform.Requests.TestHostTestFrameworkInvoker.ExecuteAsync(ITestFramework testFramework, ClientInfo client, CancellationToken cancellationToken) in /_/src/Platform/Microsoft.Testing.Platform/Requests/TestHostTestFrameworkInvoker.cs:line 62
   at Microsoft.Testing.Platform.Hosts.CommonTestHost.ExecuteRequestAsync(IPlatformOutputDevice outputDevice, ITestSessionContext testSessionInfo, ServiceProvider serviceProvider, BaseMessageBus baseMessageBus, ITestFramework testFramework, ClientInfo client) in /_/src/Platform/Microsoft.Testing.Platform/Hosts/CommonTestHost.cs:line 111
   at Microsoft.Testing.Platform.Hosts.ConsoleTestHost.InternalRunAsync() in /_/src/Platform/Microsoft.Testing.Platform/Hosts/ConsoleTestHost.cs:line 84
   at Microsoft.Testing.Platform.Hosts.ConsoleTestHost.InternalRunAsync() in /_/src/Platform/Microsoft.Testing.Platform/Hosts/ConsoleTestHost.cs:line 116
   at Microsoft.Testing.Platform.Hosts.CommonTestHost.RunTestAppAsync(CancellationToken testApplicationCancellationToken) in /_/src/Platform/Microsoft.Testing.Platform/Hosts/CommonTestHost.cs:line 85
   at Microsoft.Testing.Platform.Hosts.CommonTestHost.RunAsync() in /_/src/Platform/Microsoft.Testing.Platform/Hosts/CommonTestHost.cs:line 33
   at Microsoft.Testing.Platform.Hosts.CommonTestHost.RunAsync() in /_/src/Platform/Microsoft.Testing.Platform/Hosts/CommonTestHost.cs:line 56
   at Microsoft.Testing.Platform.Builder.TestApplication.RunAsync() in /_/src/Platform/Microsoft.Testing.Platform/Builder/TestApplication.cs:line 240

I did some digging in the code of TestNode.cs and TUnitTestFramework, but didn't find anything strange. The tests output that the detected testing platform version is 1.4.3, which defines the init prop DisplayName on TestNode, which should result in a hidden set_DisplayName(string) method, so I don't really understand how it can not find the method (or why this was not an issue previously or when targeting net9.0).

[thomhurst]

Yeah this is weird! I can replicate it too if I target .NET 6 on the build pipeline.

I've raised with the MS Testing platform team, so let's see what they say.

[thomhurst]

Seems to be a Testing Platform bug that they've identified apparently