On 19 May 2009, at 18:11, Matt Wynne wrote:
On 19 May 2009, at 14:53, Lee Longmore wrote:
I am trying to specify a controller with RSpec for the first time.
I have been using mock_model to date but, given that the models are
fully implemented, I am wondering if I should be using stub_model.
Based on what I have read, I am struggling to understand the
advantages that stub_model over mock_model might provide.
Should I be using stub_model and if so, why?
*Should* is a big word here. It depends.
When you use a stub model, you get a real instance of your AR model
object, with the database connection crippled so you can't
accidentally do something that will make your specs slow. The
benefit of this is that you get all the methods on the model
available to the controller. For example, if you have a User class
which takes a date_of_birth attribute in it's constructor, you can
call the #age method.
This can make your tests easier to read.
The cost of this is that your controller specs will be covering code
in the model classes as well as the controller you're explicitly
testing. There is a chance you'll make a change to the #age method
on your User (maybe you want to specify in days rather than years),
make the user specs pass, and check in believing you're done.
Unwittingly, you have just broken the controller specs too.
If you read what from the really experienced guys who started this
stuff off[1] say, you'll hear that mocks are really a design tool.
By creating a mock_model in your controller specs rather than
leaning on the stub_model, you're designing your 'ideal model',
rather than being constrained by whatever default methods
activerecord gives you, or you have already written. I often find
that this process drives out much more elegant interfaces onto the
models, and sometimes even shows me where I need to introduce an
intermediate class.
I think this is something you really have to play around with for
yourself to find the right balance for you and your team.
Matt Wynne
http://blog.mattwynne.net
http://www.songkick.com
[1]http://www.m3p.co.uk/blog/2009/03/08/mock-roles-not-objects-live-and-in-person/
Matt Wynne
http://blog.mattwynne.net
http://www.songkick.com
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