[rspec-users] help with test design

David Chelimsky dchelimsky at gmail.com
Wed Jun 11 15:25:23 EDT 2008

On Jun 11, 2008, at 12:06 PM, Chuck Remes wrote:

> I'm having trouble figuring out how to drive the design of a class.  
> I'm hoping I can get a hint or two from the more experienced BDDers  
> on this list.
> I'm writing an adapter class that sits between a 3rd party library  
> and my business logic. I would like to extract some information from  
> objects available from the 3rd party lib and covert them into ruby  
> objects. My desire is to insulate my ruby business logic from  
> changes in the 3rd party library by putting all of this conversion  
> code into a single adapter class (and some related "event" classes).
> Using BDD techniques I have created a pretty simple interface  to  
> the adapter class. So far the adapter class has two main public  
> methods (plus a bunch of accessors to allow the dependency injection).
> #discover_instruments
> - this method calls into the 3rd party library and pulls out the  
> 3rdPartyInstrument object and stores it off for further manipulation
> #save_components
> - this method permanently saves the 3rdPartyInstrument if it is a  
> FUTURE, or if it is a COMBINATION it iterates through each  
> sub-3rdPartyInstrument and saves it off
> Using mocks and ruby's brain-dead simple support for dependency  
> injection I have been able to mock out and verify this behavior.
> Now I need to add another public method which I will call  
> #generate_internal_instruments. What I would like this method to do  
> is iterate through my #components and create two related objects.  
> Object one will be my RubyInstrument class (called something else,  
> but this will suffice) and a second is a  
> RubyInstrumentCreationEvent. The intention is to pass the 3rdParty  
> component to RubyInstrumentCreationEvent.new(component) where it  
> will extract all salient details from the 3rdParty component (again,  
> this is for insulating the business logic from knowing this 3rd  
> Party lib). Then I will pass this RubyInstrumentCreationEvent to  
> RubyInstrument.new (or RubyInstrument.build) where it will finish  
> the construction of itself.
> Ideally, all of these steps would be private to the Adapter class  
> and would expose a single public interface called #build. All of  
> these public methods exist solely so I can test these specific  
> behaviors.
> Any suggestions on how to accomplish my goals? Is my difficulty  
> pointing at a code smell that I am not detecting?

Hey Chuck - sounds like you're trying to plan the whole process out up  
front. TDD is about discovery. Here's what I'd recommend:

Start w/ a simple example of what you want the adapter to do - the  
simplest think you can think of - when you send it the  
#generate_internal_instruments message. Get that to pass. Now the next  
simplest thing. Get that to pass. Refactor. Rinse. Repeat.

As you do this, the method might start to do too much and you'll see  
opportunities to break it up into smaller private methods or perhaps  
even methods on a brand new object you don't know about yet. That's  
all good. Let the design emerge.

If/when you do choose to move things out to other classes, you may  
want to introduce new mocks in the examples and move some of the  
examples to the group describing the new object. That's all fine.

Don't anticipate code smells, but keep sniffing. When you *do* smell  
them, deal with them immediately. Don't wait.


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