Sealing an interface after implementing it

Question

I am working on a small project and I came across that problem.

The project output is a library containing an interface. I would like to implement that interface and

Answer 1

Use an abstract base class with internal visibility. This base class is not visible outside of the library but allows you to seal the method and the class still implements the interface.

public interface ITest
{
    void SomeMethod();
}

internal abstract class SuperA : ITest
{

    public abstract void SomeMethod();

}

class A : SuperA
{
    public sealed override void SomeMethod()
    {

    }
}