<PackageReference Include="NUnit" Version="4.5.1" />

NUnit.Framework.SingleThreadedAttribute

Marks a test fixture as requiring all child tests to be run on the same thread as the OneTimeSetUp and OneTimeTearDown. A flag in the TestExecutionContext is set forcing all child tests to be run sequentially on the current thread. Any ParallelScope setting is ignored.
namespace NUnit.Framework { public class SingleThreadedAttribute : NUnitAttribute, IApplyToContext { public void ApplyToContext(TestExecutionContext context); public SingleThreadedAttribute(); } }