[rspec-users] [rspec-rails] For helper specs, why is the helper cached in the class between running each example?

Myron Marston myron.marston at gmail.com
Mon Feb 8 20:31:30 EST 2010


Thanks, David.  I searched the google group for discussions of my
problem but forgot to search the github issues.  I'll be sure to check
there next time!

On Feb 8, 5:17 pm, David Chelimsky <dchelim... at gmail.com> wrote:
> On Mon, Feb 8, 2010 at 1:44 PM, Myron Marston <myron.mars... at gmail.com> wrote:
> > I ran into a recent problem writing specs for a helper.  I was testing
> > a helper that uses the standard memoization technique of caching the
> > result of an expensive calculation in an instance variable:
>
> >  def something_expensive
> >    @something_expensive ||= do_something_expensive
> >  end
>
> > I have several different rspec examples for this one helper method,
> > all of which mock out a method that do_something_expensive calls,
> > which should in turn cause a different return value from
> > #something_expensive.  When I ran my specs, I wound up getting the
> > same return value for each spec--the return value from the first spec
> > that ran.  After investigating it a bit, I ran across this[1] code in
> > rspec-rails' ExampleHelperGroup:
>
> >        def helper
> >          self.class.helper
> >        end
>
> > The #helper method simply delegates to the class's helper method,
> > which memoizes the helper object in an instance variable.  The result
> > of this is that the helper is cached in the class between example
> > runs, and because of the memoization in my helper method, subsequent
> > specs were returning the same value.
>
> > I found a work around:
>
> >    after(:each) do
> >      helper.instance_variable_set('@something_expensive', nil)
> >    end
>
> > But it feel like a bit of a hack, and it's annoying/frustrating that I
> > have to do this.  My specs shouldn't have to be aware of the
> > memoization and manually clear it to work.
>
> > Why is the helper object cached in the class between running each
> > example?  This can accidentally lead to spec interdependencies (i.e.
> > example B only passes if it runs after example A has run, because
> > example A puts the helper object into a certain state that example B
> > unknowingly depends on).
>
> Someone just submitted a ticket w/ a patch on this last week:
>
> https://rspec.lighthouseapp.com/projects/5645-rspec/tickets/627
>
> It'll be released with rspec-rails-1.3.3, some time in the next few days.
>
> Cheers,
> David
>
>
>
> > Thanks,
> > Myron
>
> > [1]http://github.com/dchelimsky/rspec-rails/blob/1.3.2/lib/spec/rails/ex...
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