Rspec #initialize behavior

gistfile1.rb

class Foo
  attr_accessor :bar

  def initialize(bar, validator = BarValidator)
    validator.validate!(bar)
    @bar = bar
  end
end

class BarValidator
  class MissingKey < ArgumentError; end

  def self.validate!(bar)
    if !bar.has_key?(:awesome)
      raise MissingKey, "object is missing key :awesome"
    end
  end
end

describe Foo do
  let(:bar) { stub("something awesome") }

  context "when bar is valid" do
    it "assigns bar correctly" do
      validator = stub("valid validator", :validate! => true)
      Foo.new(bar, validator).bar.should == bar
    end
  end

  context "when bar is invalid" do
    it "does not instantiate an object" do
      validator = stub("valid validator")
      validator.stub(:validate!).and_raise(ArgumentError.new("Something broke"))
      expect { Foo.new(bar, validator) }.to raise_error(ArgumentError, "Something broke")
    end
  end
end

describe BarValidator do
  it "does not raise if bar has a key of :awesome" do
    expect { BarValidator.validate!(:awesome => "fuck yeah!") }.to_not raise_error
  end

  it "raises if bar is missing a key of :awesome" do
    expect { BarValidator.validate!("awesome" => "oh noes!") }.to raise_error(BarValidator::MissingKey, "object is missing key :awesome")
  end
end