MockSample.cs

using System;
using System.IO;
using System.Linq;
using Moq;
using Xunit;

namespace CSharpSample
{
    public interface IDirectory
    {
        string[] GetFileSystemEntries(string path);
        // ... more implemented methods
    }

    public class DirectoryWrapper : IDirectory
    {
        string[] IDirectory.GetFileSystemEntries(string path)
        {
            string[] entries = Directory.GetFileSystemEntries(path);
            return entries;
        }
    }

    public class DirectoryListings
    {
        private readonly IDirectory _directory;

        public DirectoryListings(IDirectory directory)
        {
            if(directory == null) throw new ArgumentNullException();
            _directory = directory;
        }

        public bool HasEntryInDirectory(string entryName, string path)
        {
            return _directory.GetFileSystemEntries(path).Contains(entryName);
        }
    }

    public class DirectoryListingsTest
    {
        private string[] _mockEntries = new string[4]{"Alpha","Bravo","Charlie","Delta"};

        [Fact]
        public void HasEntryInDirectory_ReturnsTrueIfTheAnswerContainsThePath()
        {
            var directoryMock = new Mock<IDirectory>();
            directoryMock.Setup(m => m.GetFileSystemEntries(It.IsAny<string>())).Returns(_mockEntries);
            var directoryListing  = new DirectoryListings(directoryMock.Object);
            Assert.True(directoryListing.HasEntryInDirectory("Bravo", "Some/Paht/That/Does/Not/Matter"));
        }

        [Fact]
        public void HasEntryInDirectory_ReturnsFalseIfTheAnswerDoesNotContainsThePath()
        {
            var directoryMock = new Mock<IDirectory>();
            directoryMock.Setup(m => m.GetFileSystemEntries(It.IsAny<string>())).Returns(_mockEntries);
            var directoryListing  = new DirectoryListings(directoryMock.Object);
            Assert.False(directoryListing.HasEntryInDirectory("Echo", "Some/Paht/That/Does/Not/Matter"));
        }
    }
}