<PackageReference Include="NUnit" Version="3.10.0" />

PrefixOperator

public abstract class PrefixOperator : ConstraintOperator
PrefixOperator takes a single constraint and modifies its action in some way.
namespace NUnit.Framework.Constraints { public abstract class PrefixOperator : ConstraintOperator { public override void Reduce(ConstraintBuilder.ConstraintStack stack) { stack.Push(ApplyPrefix(stack.Pop())); } public abstract IConstraint ApplyPrefix(IConstraint constraint); } }