[rspec-users] [rspec-rails] For helper specs, why is the helper cached in the class between running each example?
dchelimsky at gmail.com
Mon Feb 8 20:33:23 EST 2010
On Mon, Feb 8, 2010 at 9:31 PM, Myron Marston <myron.marston at gmail.com> wrote:
> 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!
No worries - I was just surprised that this has been a theoretical
problem for so long and three people bring it up within a week of each
other! Glad we got it visible and fixed.
> 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 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:
>> It'll be released with rspec-rails-1.3.3, some time in the next few days.
>> > Thanks,
>> > Myron
>> > http://github.com/dchelimsky/rspec-rails/blob/1.3.2/lib/spec/rails/ex...
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