[rspec-users] Varying test data

David Chelimsky dchelimsky at gmail.com
Fri Jan 11 05:50:21 EST 2008


On Jan 11, 2008 4:48 AM, Pat Maddox <pergesu at gmail.com> wrote:
>
> On Jan 11, 2008 2:33 AM, Kerry Buckley <kerry at kerrybuckley.com> wrote:
> > This isn't specific to RSpec, but is hopefully on-topic for this list.
> >
> > I like (especially when "ping pong pairing") to write a spec, then
> > write the smallest amount of code I can to pass it (especially when
> > "ping pong pairing"). Sometimes this means hard-coding a return value,
> > which means another spec is needed to prove that the code is really
> > behaving as it should. Trivial example:
> >
> > ----------
> > describe Adder do
> >    it "should add two numbers" do
> >      Adder.add(2, 2).should == 4
> >    end
> > end
> >
> > class Adder
> >    def add a, b
> >      4
> >    end
> > end
> > ----------
> > describe Adder do
> >    it "should add 2 and 2" do
> >      Adder.add(2, 2).should == 4
> >    end
> >    it "should add 3 and 4" do
> >      Adder.add(3, 4).should == 7
> >    end
> > end
> >
> > class Adder
> >    def add a, b
> >      a + b
> >    end
> > end
> > ----------
> >
> > It doesn't seem right though to have all those duplicate specs. An
> > alternative is to generate random test data, but I'm not really
> > comfortable doing that because it means the tests aren't strictly
> > repeatable. I guess this is more of a problem with classic state-based
> > testing, but even using BDD you still have to test state at the leaf
> > nodes.
> >
> > Does anyone have an opinion about whether this is a problem, and
> > whether there's a clean way of dealing with it?
>
> If I were your pair, I would smack you if you hard-coded 4 and moved
> on to the next test :)  You forgot the third step in BDD -
> refactoring!  At the simplest level, that means removing duplication.
> The duplication in this case is between the test and production code.
> In your adder example, the red/green/refactor cycle ought to go like:
>
> red - write the spec
> green - make it pass by returning 4
> refactor - generalize the method by returning the sum of the two variables
>
> Okay, I wouldn't smack you necessarily.  What you're describing here
> is a TDD technique called Triangulation.  Basically you keep writing
> tests until you have enough info to drive a useful generalization.
>
> With such a simple example, Triangulation probably isn't necessary.
> You can use Obvious Implementation (where you would just type out a +
> b to begin with - after being red first, of course), or you Fake It
> (by first returning 4 to get to green, then generalizing).
>
> Specs should give you confidence that the code works as expected.  If
> it takes you two specs to Triangulate on a solution, and the two specs
> are redundant, feel free to delete one of them.  Delete a spec if it
> doesn't add value, and keep it around if deleting it would reduce your
> confidence.
>
> I recommend reading Kent Beck's "TDD By Example" for a more in-depth
> discussion of these (and plenty other) techniques.

Apparently, Pat and I are twins separated at birth.

>
> Pat
>
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