public void Should_ReturnRow_When_SeatIsValid(string seat, int expectedRowPosition)
            {
                var sut = new BoardingPass(seat);

                Assert.That(sut.Row() == expectedRowPosition);
            }
            public void Should_ThrowException_When_NullBoardingPass()
            {
                BoardingPass sut = null;

                Assert.Throws <ArgumentNullException>(() => sut.Row());
            }