public void VisibleTill_Should_Throw_ArgumentNullException_If_Categories_Is_Null()
{
IQueryable<Category> categories = null;
DateTime tillDate = DateTime.Today;
var ex = Assert.Throws<ArgumentNullException>(() => CategoryExtensions.VisibleTill(categories, tillDate));
Assert.Equal(nameof(categories), ex.ParamName);
}
