[rspec-users] Preconditions

Pat Maddox pergesu at gmail.com
Sat Sep 8 11:18:16 EDT 2007


On 9/8/07, Wincent Colaiuta <win at wincent.com> wrote:
> El 8/9/2007, a las 2:15, Pat Maddox escribió:
>
> > * Descriptions should be broken up based on the required fixture.  I
> > don't split them up until I actually have to.  For example, if I'm
> > writing a Stack class.  I'd probably start off with
> >
> > [snip]
> >
> > For a simple spec like this it's okay.  We could factor out the
> > Stack.new call, and there's one other smell, but we'll get to that in
> > a minute.
> >
> > Now what if we want to peek the stack?
> >
> > [snip]
> >
> > Now we've got clear duplication in three places:
> >   (1) The constructor
> >   (2) Call to add_item
> >   (3) the 'it' specifier!
> >
> > It's clear that the fixture for "should not be empty" and "should let
> > you peek" are the same.  They're also different from the "should be
> > empty" so we split them up:
> >
> > [snip]
> >
> > There are two key benefits to that.  The first is that it's obvious
> > where new specifications need to go.  The behavior for #pop whether a
> > stack is empty or has an item is going to be different.  Also if you
> > need some behavior that changes with 3 items, you can probably figure
> > out that you should create a new description.
> >
> > An even bigger benefit is that it minimizes the brain processing
> > required to figure out a spec.  If you create the fixture in the setup
> > and don't vary it, it's trivial to scan through some simple
> > expectations.
> >
> > This has to do with the smell that I alluded to earlier, which was the
> > call to add_item.  Ideally your example will contain just one
> > expectation and no other setup.  This reduces the concepts that change
> > from example to example.  Change is where bugs pop up most of the
> > time.  So if you're doing setup in an example, then you probably want
> > to split it out from the current description.  In fact, in real life I
> > would have split the descriptions up immediately after writing the
> > "should not be empty" example.
>
> Brilliantly written example, very clear!
>
> +1
>
> Cheers,
> Wincent
>
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To give credit where it's due, I'm pretty sure that's from my memory
of the early examples on rspec.rubyforge.org.

Pat


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