Program.cs

using System;
using System.Reflection;
using FakeItEasy;

namespace test
{
    public class DummySettingsFactory : DummyFactory<ISettings>
    {
		static ISettings settings = new TestSettings();

        protected override ISettings Create() => settings;
    }

    public class DummyFileProviderFactory : DummyFactory<FileProvider>
    {
		static FileProvider fileProvider = A.Dummy<TestFileProvider>();

        protected override FileProvider Create() => fileProvider;
    }

    public interface ISettings
	{}

	public class RealSettings : ISettings
	{
		public RealSettings()
		{
			Console.WriteLine("ctor RealSettings");
		}
	}

	public class TestSettings : ISettings
	{
		public TestSettings()
		{
			Console.WriteLine("ctor TestSettings");
		}
	}

	public class FileProvider
	{
		public FileProvider(string basePath, ISettings settings)
		{
			// create some directories here
		}
	}

    public class TestFileProvider : FileProvider
    {
        public TestFileProvider(ISettings settings)
			: base(Assembly.GetExecutingAssembly().Location, settings)
        {
		}
    }

    public class ApplicationModule
	{
		public ApplicationModule(FileProvider fileProvider)
		{}
	}

	class Program
	{
		static void Main(string[] args)
		{
			var app = A.Fake<ApplicationModule>();

			Console.WriteLine("Hello World!");
		}
	}
}