How to Mock Public Methods in C# with NSubstitute

Source: Dev.to

Make the method virtual

This is the minimal change and fully supported by NSubstitute.

public class ProductService
{
    public virtual int GetPrice()
    {
        return 1;
    }
}

var service = Substitute.For<ProductService>();
service.GetPrice().Returns(42);

Extract an interface (cleanest design)

This is the best option.

public interface IProductService
{
    int GetPrice();
}

Inject the interface and mock it instead:

var service = Substitute.For<IProductService>();
service.GetPrice().Returns(42);

Use a wrapper / adapter (for third‑party or legacy code)

public interface IProductServiceWrapper
{
    int GetPrice();
}

public class ProductServiceWrapper : IProductServiceWrapper
{
    private readonly ProductService _service;
    public int GetPrice() => _service.GetPrice();
}

Mock ProductServiceWrapper in the same way as the interface.