public void ShouldDecreaseConcertPassesSellBy()
        {
            // arrange
            Item item = new BackstageItem(10, 9, "Backstage Passes");

            // act
            item.Process();

            // assert
            item.GetSellBy.Should().Be(8);
        }
        public void ShouldZeroConcertPassesQualityZeroDays()
        {
            // arrange
            Item item = new BackstageItem(10, 0, "Backstage Passes");

            // act
            item.Process();

            // assert
            item.GetQuality.Should().Be(0);
        }
        public void ShouldIncreaseConcertPassesQualityBy2IfTenToSixDays()
        {
            // arrange
            Item item = new BackstageItem(10, 10, "Backstage Passes");

            // act
            item.Process();

            // assert
            item.GetQuality.Should().Be(12);
        }
        public void ShouldIncreaseConcertPassesQualityBy2IfFiveToZeroDays()
        {
            // arrange
            Item item = new BackstageItem(10, 5, "Backstage Passes");

            // act
            item.Process();

            // assert
            item.GetQuality.Should().Be(13);
        }
        public void ShouldIncreaseConcertPassesQuality()
        {
            // arrange
            Item item = new BackstageItem(10, 12, "Backstage Passes");

            // act
            item.Process();

            // assert
            item.GetQuality.Should().Be(11);
        }