Take advantage of read-only generic interfaces such as IReadOnlyList, IReadOnlyDictionary, and IReadOnlyCollection to prevent modifications to collections in your .NET Core applications.

We’ll use this .NET 8 console application project to work with the IEnumerable, ICollection, IList, and IQueryable interfaces in the subsequent sections of this article.

Test projects give you a way to exercise your code to see if it works but they're also part of your project's 'permanent record.' If all you want to do is try something out with some throwaway code, C ...