CoffeePot example class in Ruby complete with Test::Unit tests.

CoffeePot.rb

#!/usr/bin/env ruby

=begin
1) When I create a "CoffeePot" object, it should be empty and I will know this because it returns true when I ask it "coffee_pot.is_empty?", and it tells me 0 when I ask it "coffee_pot.cups_left"

2) When I call the "coffee_pot.fill" method it should change state to have 10 cups left in it, so when I call the "coffee_pot.cups_left" method it returns 10.  If I ask "coffee_pot.is_empty?", it should return false.

3) every time I call the "coffee_pot.pour_cup" method, there should be one less cup remaining.

4) if I call "coffee_pot.pour_cup" when the pot is empty, it should raise an exception.
=end

require 'test/unit'

class CoffeePot
  @number_cups
  
  def initialize
    @number_cups = 0
  end

  def is_empty?
    if @number_cups == 0
      return true
    else
      return false
    end
  end

  def cups_left
    return @number_cups
  end

  def pour_cup
    if @number_cups == 0
      raise 'no cups remaining'
    else
      @number_cups -= 1
    end
  end

  def fill
    @number_cups = 10
  end
end

class CoffeePotTest < Test::Unit::TestCase
  def setup
    @empty_coffee_pot = CoffeePot.new
    @full_coffee_pot = CoffeePot.new
    @full_coffee_pot.fill
  end

  def test_is_empty?
    assert_equal true, @empty_coffee_pot.is_empty?
    assert_equal false, @full_coffee_pot.is_empty?
  end

  def test_cups_left
    assert_equal 0, @empty_coffee_pot.cups_left
    assert_equal 10, @full_coffee_pot.cups_left
  end

  def test_pour_cup
    @coffee_pot = CoffeePot.new
    @coffee_pot.fill
    @coffee_pot.pour_cup
    assert_equal 9, @coffee_pot.cups_left
    assert_raise(RuntimeError) { @empty_coffee_pot.pour_cup }
  end

  def test_fill
    @coffee_pot = CoffeePot.new
    @coffee_pot.fill
    assert_equal 10, @coffee_pot.cups_left
  end
end