On Mon, Feb 8, 2010 at 1:44 PM, Myron Marston <myron.mars...@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/example/helper_example_group.rb#L89-91
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