A mock example to illustrate the difference between mocks and dummies

mock_example_spec.rb

describe AmazonDrone do
  
  it "collects order inventory from warehouse" do
    warehouse = double(:warehouse)  
    order     = double(:order)      # dummy
    inventory = double(:inventory)  # dummy
    
    # set expectations on behavior of warehouse "mock"
    warehouse.should_receive(:fill_inventory).with(order).and_return(inventory)
    
    drone = AmazonDrone.new(warehouse)
    
    drone.collect_order_inventory(order)
    
    drone.inventory.should_not be_nil
  end
end