The crack is not showing quite yet...

gistfile1.cs

namespace RentAPlumber.Specs
{
    public class when_a_plumber_fixes_a_sink
    {
        static Plumber _plumber;
        static Sink _sink;

        Establish context = () =>
            {
                _plumber = new Plumber();
                _sink = new Sink
                    {
                        Leaks = new List<Leak>
                            {
                                new Leak(), 
                                new Leak()
                            }
                    };
            };

        Because of = () => _plumber.FixSink(_sink);

        It should_ensure_that_the_pipes_do_not_leak = () => _sink.Leaks.ShouldBeEmpty();

        It should_reveal_the_plumbers_crack = () => _plumber.CrackShowing.ShouldBeTrue();
    }
}