NewImplementation.cs

public interface IReaderWriter
{
    void Initialize();
    Data Read(int dataId);
    void Write(Data data);
}

public class FileReaderWriter : IReaderWriter
{
    public void Initialize() { throw new NotImplementedException(); }

    public Data Read(int dataId) { throw new NotImplementedException(); }

    public void Write(Data data) { throw new NotImplementedException(); }
}