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

NUnit.Framework.Constraints.SelfResolvingOperator

public abstract class SelfResolvingOperator : ConstraintOperator
Abstract base class for operators that are able to reduce to a constraint whether or not another syntactic element follows.
namespace NUnit.Framework.Constraints { public abstract class SelfResolvingOperator : ConstraintOperator { protected SelfResolvingOperator(); } }