grow a test suite

walrus.rb

class Walrus
  attr_reader :energy

  def initialize
    @energy = 0
  end

  def receive_gift!(gift)
   if gift.edible?
     @energy += gift.digest.energy
   end 
  end
end

class LifeEvent
  attr_reader :energy
  def initialize(params)
    @energy = params.fetch(:energy)
  end
end

describe Walrus do
  it "gains energy from eatable things" do
    cheese = stub( :edible? => true , :digest => LifeEvent.new(:energy => 100)) 
    expect do
      subject.receive_gift!(cheese)
    end.to  change {subject.energy }.by(100)
  end
  
  it "does not gain energy form non-foof" do
    shoe =  stub(:edibile? => false)
    expect do
      subject.receive_gift!(shoe)
    end.not_to  { subject.energy }
  end
end