PromotionalPurchaseSpecification.cs

public class PromotionalPurchaseSpecification : Specification<PurchaseTestInput>
{
    private readonly PurchaseTestInput purchaseTestInput;

    public PromotionalPurchaseSpecification(PurchaseTestInput purchaseTestInput)
    {
        this.purchaseTestInput = purchaseTestInput;
    }

    public override bool IsSatisfiedBy(PurchaseTestInput entity)
    {
        return this.purchaseTestInput.IsPromotionalPurchase && this.purchaseTestInput.TotalPrice < 5;
    }
}