From: Jake McArthur <jake.mcarthur@...>
Date: 2006-05-16T07:26:11+09:00
Subject: Re: BDD and mocking objects

I say it _does_ matter. Behavior driven development, in particular,  
emphasizes testing the way that objects interact. As such, it should  
be tested that the Rental class is treating the Movie class properly.  
Think of it this way. What if you decided there should be another  
type of object that has a similar interface to a Movie object? You  
don't want your Rental tests to be locked to the Movie class since  
you want to be able to pass in the other kind of object as well. The  
only way to test that is with mock objects. Other reasons for mocking  
could include an incomplete or buggy implementation of the Movie  
class and better specification of what the roles and responsibilities  
of each object are in the program.

- Jake McArthur

On May 15, 2006, at 5:08 PM, Pat Maddox wrote:

> Brian Hughes discussed BDD [1] in a recent post, which piqued my
> interest enough to check out RSpec.  I used his idea and went through
> the first chapter of Refactoring to learn the rspec ropes.
>
> The most interesting stuff is the specs for Customer, but they're kind
> of long, so I'm going to show a less interesting spec.
>
> context "A new rental" do
>  setup do
>    @movie = Movie.new("New Movie", Movie::REGULAR)
>    @rental = Rental.new(@movie, 3)
>  end
>
>  specify "should have a movie and rental length" do
>    @rental.movie.should_be @movie
>    @rental.days_rented.should_be 3
>  end
> end
>
> I'm wondering if I should be using a mock instead of creating a new
> Movie object in setup.  This is a trivial example and perhaps it would
> be unnecessary, but I want to know if I "get it."  I'm testing a
> Rental's behavior, so I really don't care about how a Movie behaves.
> As long as my Rental gets an object that behaves the same way a movie
> does, it should be happy.  In this case, I don't care about a Movie's
> title or code, so I could pass in a nil object if I wanted to.  Would
> I want to mock the @movie then?  Doesn't matter much in this
> particular case, but assume that one of my Rental methods relied on a
> method or two of Movie.
>
> Thanks for any input.
>
> Pat
>
> [1] http://www.ruby-forum.com/topic/65640#77053
>