Concrete Command (AddTextCommand):?

Short answer: The AddTextCommand is a concrete implementation of the ICommand interface. It encapsulates the request to add text to the document. The Execute() method adds the specified text to the document, and the Undo() method removes that text. public class AddTextCommand : ICommand

Example code

{
private readonly Document _document;
private readonly string _text;
public AddTextCommand(Document document, string text)
{
_document = document;
_text = text;
}
public void Execute() => _document.AddText(_text);
public void Undo() => _document.RemoveText(_text);
}

Real-world example (ShopNest)

Use a GoF pattern in ShopNest only when it removes duplication or makes a change safer—explain the problem it solves in the interview.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.