Do the Splits

animal.rb

module Sustenance
  def initialize
    @stomach = []
    super
  end

  def eat(food)
    @stomach << { food: food }
  end

  def drink(drink)
    @stomach << { drink: drink }
  end

  def poop
    digest_to_completion(:food, "can't poop")
  end

  def pee
    digest_to_completion(:drink, "can't pee")
  end

  private

  def digest_to_completion(kind, error_message)
    victuals = @stomach.select { |v| v[kind] }

    if victuals.empty?
      raise error_message
    end

    @stomach = @stomach - victuals
  end
end

class Dog
  module Communication
    def bark
      "Woof"
    end

    def growl
      "Grrr"
    end

    def wimper
      "Rrrr"
    end
  end

  include Communication
  include Sustenance
end

class Cat
  include Sustenance
end

# Testing!

require 'minitest/autorun'

class TestDog < Minitest::Test
  def setup
    @dog = Dog.new
  end

  def test_bark
    assert_equal @dog.bark, 'Woof'
  end

  # Tests ommited...
end

class TestSustenance < Minitest::Test
  class Animal
    include Sustenance
    attr_reader :stomach
  end

  def setup
    @animal = Animal.new
  end

  def test_eat
    assert_empty @animal.stomach
    @animal.eat("pepper")
    refute_empty @animal.stomach
  end

  def test_drink
    assert_empty @animal.stomach
    @animal.drink("slurppy")
    refute_empty @animal.stomach
  end

  def test_poop
    @animal.eat("sand")
    refute_empty @animal.stomach
    @animal.poop
    assert_empty @animal.stomach
  end

  def test_pee
    @animal.drink("soda")
    refute_empty @animal.stomach
    @animal.pee
    assert_empty @animal.stomach
  end
end