public void ErrorifDifferentRule() { var sut = new RentZeroSurcharger(); var lse = LeaseWithPenaltyRate(0.03M); lse.Rent.PenaltyRule = "a different rule"; sut.Invoking(_ => _.GetPenalties(lse, 3.May(2018), 123)) .Should().Throw <BadKeyException>(); }