Deployment item doesn't work well when app domain is disabled

[Youssef1313]

This is a bug dating back to the oldest stable MSTest version on nuget.org. The two features never worked correctly together.

TestProject44.zip

Run with dotnet test -- RunConfiguration.DisableAppDomain=true:

• All versions: The test assembly is loaded twice in the same app domain. Once from bin and once from deployment directory

  

• Up to 3.10.5: The test fails with InvalidCastException:

      Example (10s 862ms): Error Message: Test method TestProject44.Test1.Example threw exception:
      System.InvalidCastException: [A]ExampleDataType cannot be cast to [B]ExampleDataType. Type A originates from 'TestProject44, Version=1.0.0.0, Culture=neutral, Pub
      licKeyToken=null' in the context 'LoadFrom' at location 'C:\Users\ygerges\source\repos\TestProject44\TestProject44\TestResults\Deploy_ygerges 2025-10-14 11_24_27\
      Out\TestProject44.dll'. Type B originates from 'TestProject44, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' in the context 'Default' at location 'C:\Use
      rs\ygerges\source\repos\TestProject44\TestProject44\bin\Debug\net48\TestProject44.dll'.
      Stack Trace:
          at TestProject44.Test1.ExampleDataTypeTypeConverter.ConvertTo(ITypeDescriptorContext context, CultureInfo culture, Object value, Type destinationType) in C:\U
      sers\ygerges\source\repos\TestProject44\TestProject44\Test1.cs:line 33
         at TestProject44.Test1.Example() in C:\Users\ygerges\source\repos\TestProject44\TestProject44\Test1.cs:line 17
  

• 3.11.0 and 4.0.0: the test passes, even if the assembly is still loaded twice. That might get broken as it was before again when Fix deployment regression #6718 is merged.

[Youssef1313]

FYI @stan-sz