public void ShouldThrowExceptionWhenColumnsIsNull()
            {
                ITemplate template = new ImageCarouselTemplate();

                ExceptionAssert.Throws <InvalidOperationException>("The columns cannot be null.", () =>
                {
                    template.Validate();
                });
            }
            public void ShouldThrowExceptionWhenColumnsIsInvalid()
            {
                ITemplate template = new ImageCarouselTemplate()
                {
                    Columns = new[]
                    {
                        new ImageCarouselColumn()
                    }
                };

                ExceptionAssert.Throws <InvalidOperationException>("The image url cannot be null.", () =>
                {
                    template.Validate();
                });
            }