public void Id_is_returned_if_it_is_not_mapped_to_url() {
var sut = new UrlMapping();
var url = sut.Url_for_id("unknown");
Assert.That(url, Is.EqualTo("unknown"));
}
public void Id_is_mapped_back_to_url() {
var sut = new UrlMapping();
var id = sut.Id_for_Url("a");
var url = sut.Url_for_id(id);
Assert.That(url, Is.EqualTo("a"));
}