mocha developer - Sep 2006 - I''m misunderstanding how stubs works

We''re still just starting out with Mocha/Stubba, so please forgive any
newbie errors.

I''m using "stubs" to test some realtime functions, to control
exactly which
time is returned from Time.now. I would expect the following test to pass:

  def test_two_stubs
    t = Time.now - 60
    Time.stubs(:now).returns(t)

    start_time = Time.now

    t += 20
    Time.stubs(:now).returns(t)

    end_time = Time.now

    assert_equal end_time - start_time, 20
  end

But it fails with:

  1) Failure:
test_two_stubs(MochaTest) [mochatest.rb:19]:
<0.0> expected but was
<20>.

I can create a test which works as I intend:

  def test_lambda
    t = Time.now - 60
    Time.stubs(:now).returns(lambda { t })

    start_time = Time.now

    t += 20

    end_time = Time.now

    assert_equal end_time - start_time, 20
  end

But I''d be interested to understand why the first version
doesn''t.

Thanks in advance for any help you can offer!

-------------------------------------------------
Paul Butcher
CTO
RE5ULT Limited
74 Eden Street,
Cambridge
CB1 1EL
http://www.82ask.com/

Office: +44 (0) 1223 309080
Mobile: +44 (0) 7740 857648
Email: paul at 82ask.com
MSN: paul at paulbutcher.com
AIM: paulrabutcher
Skype: paulrabutcher
LinkedIn: https://www.linkedin.com/in/paulbutcher
-------------------------------------------------

82ASK: text any question to 82ASK (82275) and get the answer in minutes.
Visit www.82ask.com to get your first 2 questions answered for free.

On 23/09/06, Paul Butcher <paul at 82ask.com>
wrote:
>
> I''m using "stubs" to test some realtime functions, to
control exactly
> which
> time is returned from Time.now. I would expect the following test to pass:
>
>   def test_two_stubs
>     t = Time.now - 60
>     Time.stubs(:now).returns(t)
>
>     start_time = Time.now
>
>     t += 20
>     Time.stubs(:now).returns(t)
>
>     end_time = Time.now
>
>     assert_equal end_time - start_time, 20
>   end
>
> But it fails with:
>
>   1) Failure:
> test_two_stubs(MochaTest) [mochatest.rb:19]:
> <0.0> expected but was
> <20>.
>
> I can create a test which works as I intend:
>
>   def test_lambda
>     t = Time.now - 60
>     Time.stubs(:now).returns(lambda { t })
>
>     start_time = Time.now
>
>     t += 20
>
>     end_time = Time.now
>
>     assert_equal end_time - start_time, 20
>   end
>
> But I''d be interested to understand why the first version
doesn''t.
>
Hi Paul,

The first version doesn''t work, because the second stub expectation
doesn''t
replace the first. When the end_time call to Time.now comes in, it is
matched to the first expectation and so returns the first value of t. I
agree that this is not what you would expect and it''s been on my todo
list
for a while. It hasn''t made it to the top, because there are ways round
it
as you have demonstrated. I would probably use the same technique as you,
but you might be interested to see a couple of other possibilities...

The first one makes use of the fact that expectations match based on
parameters as well as method name. Even though Time.now doesn''t take
any
parameters, you can supply a block which returns true or false depending on
whether it should match...

  def test_two_stubs_with_parameter_block
    t = Time.now - 60
    context = :start
    Time.stubs(:now).with { context == :start }.returns(t)
    Time.stubs(:now).with { context == :finish }.returns(t + 20)

    start_time = Time.now

    context = :finish

    end_time = Time.now

    assert_equal end_time - start_time, 20
  end

The second one makes use of a recent change in HEAD (not released in the
gem), which allows you to specify consecutive return values. Although this
won''t be useful if there are many calls to Time.now...

  def test_two_stubs_consecutive_return_values
    t = Time.now - 60

    Time.stubs(:now).returns(t, t + 20)

    start_time = Time.now

    end_time = Time.now

    assert_equal end_time - start_time, 20
  end

I hope that helps.
-- 
James.
http://blog.floehopper.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://rubyforge.org/pipermail/mocha-developer/attachments/20060923/4af3a085/attachment.html

James Mead wrote:
> The first version doesn''t work, because the second stub
expectation
> doesn''t replace the first. When the end_time call to Time.now
comes in,
> it is matched to the first expectation and so returns the first value
> of t. I agree that this is not what you would expect and it''s been
on
> my todo list for a while. It hasn''t made it to the top, because
there
> are ways round it as you have demonstrated. I would probably use the
> same technique as you, but you might be interested to see a couple of
> other possibilities... 
Cool. Thanks James - that makes perfect sense. Glad to see that I''m not
being stupid ;-)

Cheers!

-------------------------------------------------
Paul Butcher
CTO
RE5ULT Limited
74 Eden Street,
Cambridge
CB1 1EL
http://www.82ask.com/

Office: +44 (0) 1223 309080
Mobile: +44 (0) 7740 857648
Email: paul at 82ask.com
MSN: paul at paulbutcher.com
AIM: paulrabutcher
Skype: paulrabutcher
LinkedIn: https://www.linkedin.com/in/paulbutcher
-------------------------------------------------

82ASK: text any question to 82ASK (82275) and get the answer in minutes.
Visit www.82ask.com to get your first 2 questions answered for free.