# BDD and mocking objects

**URL:** <https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830>\
**Category:** Ruby\
**Created:** [May 16, 2006, 12:11am UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830 "2006-05-16T00:11:15Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 12:11am UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830/1 "2006-05-16T00:11:15Z")

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Brian H. 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] [Is test driven development for newbies? - Rails - Ruby-Forum](http://www.ruby-forum.com/topic/65640#77053)

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 12:26am UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830/2 "2006-05-16T00:26:54Z")

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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

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 12:45am UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830/3 "2006-05-16T00:45:23Z")

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Thanks for the reply Jake. Very good points, and in fact they  
basically opened my eyes to a problem that I run into when doing TDD.  
If I were to write this system from scratch, focusing on behavior, my  
process would go something like this:

1. Decide to write the Rental class
2. Realize that Rental depends on Movie
3. Write the Movie class
4. Write the Rental class

Again, this is a trivial example, so perhaps the problem here is  
non-obvious (to others, I have a feeling you can see it immediately).  
At this point I don’t care about a Movie, I only care about a Rental  
and its behavior. The way I’ve done things though requires me to  
write the Movie class before I even begin working on the Rental’s  
behavior. First of all that sidetracks me for a bit while I write  
Movie and its tests, and in general I think it leads to me writing  
more tightly coupled code.

It seems obvious to me now that when writing a unit test, I should  
mock out any relationships, so basically any object that’s not the one  
I’m explicitly testing. I’m sure there are exceptions, but does that  
seem like a good guideline to follow?

Pat

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 1:19am UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830/4 "2006-05-16T01:19:38Z")

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Yes, I would say that is a good guideline in general. For the record,  
I am not a BDD guru by any means, though I have been using BDD  
techniques for some time now when using TDD. I have been using RSpec  
for roughly a month now, I think.

- Jake McArthur

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 1:34am UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830/5 "2006-05-16T01:34:56Z")

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I’ve been doing lots of reading this afternoon, and came across a few  
comments that leave me with more questions.

Dave A. said in a podcast that RSpec doesn’t take the place of  
functional or integration tests.  
Martin F. wrote that you must use coarse grained acceptance tests.

I simply don’t know what functional, integration, and acceptance tests  
are, and how they differ from unit tests. Where can I find some info  
on why I should use them, and how to use them effectively?

Pat

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 8:39pm UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830/6 "2006-05-16T20:39:17Z")

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On May 15, 2006, at 3:42 PM, Pat M. wrote:

> The way I’ve done things though requires me to write the Movie  
> class before I even begin working on the Rental’s behavior. First  
> of all that sidetracks me for a bit while I write Movie and its  
> tests, and in general I think it leads to me writing more tightly  
> coupled code.

How does it make your code more coupled?

> It seems obvious to me now that when writing a unit test, I should  
> mock out any relationships, so basically any object that’s not the one  
> I’m explicitly testing. I’m sure there are exceptions, but does that  
> seem like a good guideline to follow?

I typically only stub methods, typically overriding superclass  
methods in a subclass.

For example, I’ll be using open-uri (which overrides Kernel#open) in  
my implementation then add a MyClass#open stub that allows me to  
provide the open behavior that open-uri gives. I’ve done the same  
with #system and #`.

For me, mocks feel like a lot of typing for something I can achieve  
more simply by exploiting Ruby’s dynamic language features.

–  
Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net)  
This implementation is HODEL-HASH-9600 compliant

[http://trackmap.robotcoop.com](http://trackmap.robotcoop.com)

---

<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 8:42pm UTC](https://www.ruby-forum.com/t/bdd-and-mocking-objects/94830/7 "2006-05-16T20:42:55Z")

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On May 15, 2006, at 4:33 PM, Pat M. wrote:

> I’ve been doing lots of reading this afternoon, and came across a few  
> comments that leave me with more questions.
> 
> Dave A. said in a podcast that RSpec doesn’t take the place of  
> functional or integration tests.

[http://c2.com/cgi/wiki?FunctionalTest](http://c2.com/cgi/wiki?FunctionalTest)

[http://c2.com/cgi/wiki?IntegrationTest](http://c2.com/cgi/wiki?IntegrationTest)

> Martin F. wrote that you must use coarse grained acceptance tests.

[http://c2.com/cgi/wiki?AcceptanceTest](http://c2.com/cgi/wiki?AcceptanceTest)

> I simply don’t know what functional, integration, and acceptance tests  
> are, and how they differ from unit tests. Where can I find some info  
> on why I should use them, and how to use them effectively?

The c2 wiki has descriptions from the best minds in the business.

–  
Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net)  
This implementation is HODEL-HASH-9600 compliant

[http://trackmap.robotcoop.com](http://trackmap.robotcoop.com)