Changing Our Design to Support Testing

Our new code represents a small change to the design of the system. Before, the Http instance was created by the retrieve() method as a private detail of the AddressRetriever class. Now, any client that interacts with AddressRetriever is responsible for creating and passing in an appropriate Http instance. Perhaps something like:

AddressRetriever retriever = new AddressRetriever(new HttpImpl());

Ways to inject stubs