using System;

using System.Collections.Generic;

using System.Collections;

using NUnitLite;

using NUnit.Framework;

using System.Linq;

using NSubstitute;

​

new AutoRun().Execute(new[]{"--nocolor"});

​

public abstract class AbstractGenerator

{

    public abstract IEnumerable<int> Generate();

}

​

public class ConcreteAbstract : AbstractGenerator

{

    public override IEnumerable<int> Generate() => [2, 3, 4];

}

​

public interface IGenerator 

{

    IEnumerable<int> Generate();

}

​

public class ConcreteInterface : IGenerator

{

    public IEnumerable<int> Generate() => [2, 3, 4];

}

​

public class Test

{

    [Test]

    public void TestWithAbstract()

    {

        var generator = Substitute.For<AbstractGenerator>();

        generator.Generate().Returns([1, 2, 3]);

        Assert.That(Sum(generator), Is.EqualTo(6));

    }

    [Test]

    public void TestWithConcreteAbstract()

    {

        var generator = Substitute.For<ConcreteAbstract>();

        generator.Generate().Returns([1, 2, 3]);

        Assert.That(Sum(generator), Is.EqualTo(6));

    }

    [Test]

    public void TestWithInterface()

    {

        var generator = Substitute.For<IGenerator>();

        generator.Generate().Returns([1, 2, 3]);

        Assert.That(Sum(generator), Is.EqualTo(6));

    }

    [Test]

    public void TestWithConcreteInterface()

    {

        var generator = Substitute.For<ConcreteInterface>();

        generator.Generate().Returns([1, 2, 3]);

        Assert.That(Sum(generator), Is.EqualTo(6));

    }

    private static int Sum(AbstractGenerator generator) => generator.Generate().Sum();

    private static int Sum(IGenerator generator) => generator.Generate().Sum();

}