gistfile1.rb

describe AccountService, "#transfer" do
  before(:each) do
    @from = Account.new 500
    @to = Account.new 100
    @service = AccountService.new
  end

  def do_transfer
    @service.transfer @from, @to, 150
  end

  it "state-based" do
    do_transfer
    @from.balance.should == 350
    @to.balance.should == 250
  end

  it "interaction-based" do
    @from.should_receive(:debit).with(150)
    @to.should_receive(:credit).with(150)
    do_transfer
  end
end