GreenIcicle

private Controller CreateSubject(
            string[] names = null,
            IDataSource dataSource = null)
{
    names = names ?? new[] { "Alice", "Bob", "Alfred" };
    if (dataSource == null)
    {
        var mock = new Mock<IDataSource>();
        mock.Setup(x => x.GetNames()).Returns(names);
        dataSource = mock.Object;

GreenIcicle

internal class ControllerBuilder
{
    private IDataSource _dataSource;
    private IEnumerable<string> _names = new[] {"Alice", "Bob", "Alfred"};

    public ControllerBuilder WithDataSource(IDataSource dataSource)
    {
        _dataSource = dataSource;
        return this;
    }

GreenIcicle

[Fact]
public void Sort_by_first_letter()
{
    // Arrange
    var dataSource = new Mock<IDataSource>();
    dataSource.Setup(x => x.GetNames()).Returns(new[] {"Alice", "Bob", "Alfred"});
    var subject = new Controller(dataSource.Object);
 
    // Act
    subject.Filter("a");

GreenIcicle

using System.Collections;
using System.Collections.Generic;
using System.Linq;

namespace GreenIcicle
{
    public class ByteArray : IEnumerable<byte>
    {
        private readonly IEnumerable<byte> bytes;

GreenIcicle

// Moves a directory up some levels.
// Can/should be changed to an extension method on DirectoryInfo.
        private DirectoryInfo Up(DirectoryInfo directory, int levels)
        {
            while (levels > 0 && directory != null)
            {
                directory = directory.Parent;
                levels--;
            }