geometry.rb

RSpec.configure do |config|
  # Use color in STDOUT
  config.color_enabled = true

  # Use color not only in STDOUT but also in pagers and files
  config.tty = true

  # Use the specified formatter
  config.formatter = :progress # :progress, :html, :textmate
end

module SimplePolygon
  def area
    @base * @height
  end

  def perimeter
    (@base * 2) + (@height * 2)
  end
end

#implement a Rectangle class that includes functionality from SimplePolygon
class Rectangle

end

#implement Square. It should inherit from Rectangle
#and contain no code other than an initialize method
class Square

end

#Implement Triangle. It should include SimplePolygon
#and override area and perimeter as needed.
#hint: the result of SimplePolygon area is usable to
#find a triangle's area. The result of SimplePolygon
#perimeter is not

class Triangle

end

describe Rectangle do
  it "knows its area" do
    Rectangle.new(3,5).area.should eq(15)
  end

  it "knows its perimeter" do
    Rectangle.new(3,5).perimeter.should eq(16)
  end
end

describe Square do
  it "is a Rectangle" do
    Square.new(5).class.superclass.should eq(Rectangle)
  end

  it "knows its area" do
    Square.new(5).area.should eq(25)
  end

  it "knows its perimeter" do
    Square.new(5).perimeter.should eq(20)
  end
end

describe Triangle do
  it "knows its area" do
    Triangle.new(4,4,4).area.should eq(8)
  end

  it "knows its perimeter" do
    Triangle.new(4,4,4).perimeter.should eq(12)
  end

  context "utlizing SimplePolygon" do

    before(:each) do
      #monkeypatch SimplePolygon to control area
      #you'd never do this in real life but it's
      #the only way to make this test work
      module SimplePolygon
        def area
          100
        end

        def perimeter
          throw Exception
        end
      end

      @triangle = Triangle.new(4,4,4)
    end

    it "utilizes the area method" do
      @triangle.area.should eq(50)
    end

    it "completely overrides the perimeter method" do
      @triangle.perimeter.should eq(12)
    end
  end
end