public void CanReturnNullIfNeitherDogNorCatPassedInAsPreferredAnimal() { // Arrange AnimalNode <string> badPreference = new AnimalNode <string>("bird"); AnimalNode <string> legitPreference = new AnimalNode <string>("cat"); AnimalShelter <string> animalShelter = new AnimalShelter <string>(); animalShelter.EnqueueAnimal(legitPreference); // Act AnimalNode <string> dequeuedAnimal = animalShelter.DequeueAnimal(badPreference); // Assert Assert.Null(dequeuedAnimal); }