mocha developer - Sep 2006 - Problem stubbing instances referred to by constants

Hi James,

An instance retains its mocha between tests if that instance is
pointed to by a constant.  The simplest failing test is something like
(add as a new file in mocha/test)..

#--code--

require File.join(File.dirname(__FILE__), "test_helper")

require ''stubba''

class WemStubbaTest < Test::Unit::TestCase

  Arr = [1, 2, 3]

  def test_a
    Arr.stubs(:size).returns(6)
    assert_equal 6, Arr.size
  end

  def test_b
    assert_equal 3, Arr.size #=> Failing test when both tests run
consecutively
  end

end

#--/code--

I got as far as noticing that Stubba::InstanceMethod#unstub is
''intentionally empty''.  This is fine for most object instances
but not
ones that hang around (like the array above).  Sadly, I don''t have (or
even know whether there should be) a fix.

Chris

On 25/09/06, Chris Roos <chrisjroos at gmail.com>
wrote:
>
> Hi James,
>
> An instance retains its mocha between tests if that instance is
> pointed to by a constant.  The simplest failing test is something like
> (add as a new file in mocha/test)..
>
> #--code--
>
> require File.join(File.dirname(__FILE__), "test_helper")
>
> require ''stubba''
>
> class WemStubbaTest < Test::Unit::TestCase
>
>   Arr = [1, 2, 3]
>
>   def test_a
>     Arr.stubs(:size).returns(6)
>     assert_equal 6, Arr.size
>   end
>
>   def test_b
>     assert_equal 3, Arr.size #=> Failing test when both tests run
> consecutively
>   end
>
> end
>
> #--/code--
>
> I got as far as noticing that Stubba::InstanceMethod#unstub is
> ''intentionally empty''.  This is fine for most object
instances but not
> ones that hang around (like the array above).  Sadly, I don''t have
(or
> even know whether there should be) a fix.
>
Hi Chris,

I''m pretty sure the solution is just to make InstanceMethod even more
like
ClassMethod in #stub & #unstub. I think the difference was only ever an
optimization with the assumption that instances wouldn''t persist
between
tests.

However, I also wonder if this scenario is itself a code smell i.e. I''m
not
sure anything should persist between tests - but maybe your actual scenario
involves a constant within an external class...?

I''ll try to have a look at it soon.
Thanks.
-- 
James.
http://blog.floehopper.org
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On 9/25/06, James Mead <jamesmead44 at gmail.com>
wrote:
> On 25/09/06, Chris Roos <chrisjroos at gmail.com> wrote:
> > Hi James,
> >
> > An instance retains its mocha between tests if that instance is
> > pointed to by a constant.  The simplest failing test is something like
> > (add as a new file in mocha/test)..
> >
> > <snipped code>
> >
> > I got as far as noticing that Stubba::InstanceMethod#unstub is
> > ''intentionally empty''.  This is fine for most object
instances but not
> > ones that hang around (like the array above).  Sadly, I don''t
have (or
> > even know whether there should be) a fix.
> >
>
> Hi Chris,
>
> I''m pretty sure the solution is just to make InstanceMethod even
more like
> ClassMethod in #stub & #unstub. I think the difference was only ever an
> optimization with the assumption that instances wouldn''t persist
between
> tests.
>
You''re right, of course.  As a quick check, I removed the over-ridden
methods (InstanceMethod#stub and InstanceMethod#unstub) and the
failing test provided originally passes.
> However, I also wonder if this scenario is itself a code smell i.e.
I''m not
> sure anything should persist between tests - but maybe your actual scenario
> involves a constant within an external class...?
>
Hmm, not too sure really.  We have a constant that gets set to an
instance of two possible classes at rails start time (e.g. Foo Bar.new OR Foo =
Baz.new).  I guess we''re providing singleton''ish
access to the instantiated object.

Chris

On 26/09/06, Chris Roos <chrisjroos at gmail.com>
wrote:
>
> You''re right, of course.  As a quick check, I removed the
over-ridden
> methods (InstanceMethod#stub and InstanceMethod#unstub) and the
> failing test provided originally passes.
>
Thanks for the patch - I''ve committed it.
-- 
James.
http://blog.floehopper.org
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