<PackageReference Include="NUnit" Version="4.2.2" />

NUnit.Framework.Internal.Builders.NUnitTestFixtureBuilder

NUnitTestFixtureBuilder is able to build a fixture given a class marked with a TestFixtureAttribute or an unmarked class containing test methods. In the first case, it is called by the attribute and in the second directly by NUnitSuiteBuilder.
namespace NUnit.Framework.Internal.Builders { public class NUnitTestFixtureBuilder { public TestSuite BuildFrom(ITypeInfo typeInfo, IPreFilter filter); public TestSuite BuildFrom(ITypeInfo typeInfo, IPreFilter filter, ITestFixtureData testFixtureData); public NUnitTestFixtureBuilder(); } }