Rails - Aug 2006 - A mock which extends rather than replaces a class?

While running tests, we would like to instrument some of the classes 
under test. We still want the classes to do exactly what they currently 
do, but we would like them to do more when running in the test 
environment.

Clearly we can (and currently do) just extend the objects "on the fly"
where necessary, but this is a bit messy - we''d like some centralised 
way to always extend the objects for all tests. Is there any way of 
using the test/mocks directory to achieve this? We can''t see any way to
use it to do anything other than completely replace a class.

Thanks in advance!

paul.butcher->msgCount++

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Posted via http://www.ruby-forum.com/.

On 14/08/06, Paul Butcher <paul@paulbutcher.com>
wrote:
> While running tests, we would like to instrument some of the classes
> under test. We still want the classes to do exactly what they currently
> do, but we would like them to do more when running in the test
> environment.
>
> Clearly we can (and currently do) just extend the objects "on the
fly"
> where necessary, but this is a bit messy - we''d like some
centralised
> way to always extend the objects for all tests. Is there any way of
> using the test/mocks directory to achieve this? We can''t see any
way to
> use it to do anything other than completely replace a class.
I''m not sure it''s exactly what you''re looking for,
but you might find
the Stubba component of Mocha(http://mocha.rubyforge.org) useful. It
allows you to temporarily (for the duration of the test method)
replace method implementations with simple stubs which return a known
value.

James Mead.
http://blog.floehopper.org

Paul Butcher wrote:
> While running tests, we would like to instrument some of the classes 
> under test. We still want the classes to do exactly what they currently 
> do, but we would like them to do more when running in the test 
> environment.
> 
> Clearly we can (and currently do) just extend the objects "on the
fly"
> where necessary, but this is a bit messy - we''d like some
centralised
> way to always extend the objects for all tests. Is there any way of 
> using the test/mocks directory to achieve this? We can''t see any
way to
> use it to do anything other than completely replace a class.
> 
> Thanks in advance!
> 
> paul.butcher->msgCount++
Have you considered Stubba? It comes with the Mocha library.

http://mocha.rubyforge.org/

-- 
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Luke Redpath wrote:
> Have you considered Stubba? It comes with the Mocha library.
> 
> http://mocha.rubyforge.org/
I''ve not come across Stubba before - it looks rather nice!
Unfortunately
I''m not sure that it gives us what we''re after in this
particular case
(please forgive me if I''m missing something). Maybe an example will 
help.

What our current tests do is something along the following lines. Given 
a class:

class Foo
  def frobnicate
    # Long and complicated code...
  end

  def gimbalize
    # More complicated stuff...
  end
end

We have tests which do something along the following lines:

module InstrumentedFoo
  attr_reader was_frobnicated
  def frobnicate
    super
    @was_frobnicated = true
  end
end

module InterceptFooCreation
  def new(options = {})
    foo = super options
    foo.extend InstrumentedFoo
    return foo
  end
end

def test_something
  Foo.extend InterceptFooCreation
  foo = ... obtain a foo somehow ...
  assert foo.was_frobnicated
end

This all works, but is not exactly pleasant. What we would like is some 
means by which we can ensure that *every* Foo object is instrumented 
while running tests.

We can trivially achieve this using the test/mocks directory, as long as 
we don''t mind completely replacing our Foo class, but it
doesn''t seem to
help if we just want to extend the Foo class as above...

Suggestions gratefully received!

paul.butcher->msgCount++

-- 
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Perhaps decorating your foo object and then creating a class method on 
Foo to return the decorated object would work?

class InstrumentedFoo
  attr_reader :was_frobnicated

  def initialize(original_foo)
    @foo = original_foo
  end

  def frobnicate
    @foo.frobnicate
    @was_frobnicated = true
  end

  # proxy other methods to original foo
  def method_missing(method, *args)
    @foo.send(method, *args)
  end
end

Foo.stubs(:instrumented_instance).returns(InstrumentedFoo.new(Foo.new))

# example
@foo = Foo.instrumented_instance
@foo.gimbalize # still calls Foo#gimbalize
@foo.frobnicate # calls Foo#frobnicate
assert @foo.was_frombnicated

Or is that still not what you are after?

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Luke Redpath wrote:
> Perhaps decorating your foo object and then creating a class method on 
> Foo to return the decorated object would work?
> 
> <snip>
>
> Or is that still not what you are after?
That would work fine if the test has control over the creation of the 
object. But I''m not sure that it helps if its the code under test which
creates the object (which is the situation we''re in).

Thanks!

paul.butcher->msgCount++

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On 14/08/06, Paul Butcher <paul@paulbutcher.com>
wrote:
> That would work fine if the test has control over the creation of the
> object. But I''m not sure that it helps if its the code under test
which
> creates the object (which is the situation we''re in).
Can you give a simple example of what you''re trying to do?
It''s much
easier discussing specifics.

Stubba allows you to stub any class method including "new" along the
following lines.

def test_me
  Employee.stubs(:new).returns(anything_you_want)
  company = Company.new
  company.do_something_which_calls_new_on_employee
  assert_something
end

James
http://blog.floehopper.org

Paul Butcher wrote:
> While running tests, we would like to instrument some of the classes 
> under test. We still want the classes to do exactly what they currently 
> do, but we would like them to do more when running in the test 
> environment.
> 
> Clearly we can (and currently do) just extend the objects "on the
fly"
> where necessary, but this is a bit messy - we''d like some
centralised
> way to always extend the objects for all tests. Is there any way of 
> using the test/mocks directory to achieve this? We can''t see any
way to
> use it to do anything other than completely replace a class.
> 
> Thanks in advance!
> 
> paul.butcher->msgCount++
Rails can do this easily, you just have to require_dependency on the 
file in question and THEN reopen the class to change it.

#test/mocks/test/foo.rb
require_dependency "#{RAILS_ROOT}/lib/foo.rb"
class Foo
  def bar
    ...
  end
end


-- 
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On 14/08/06, James Mead <jamesmead44@gmail.com>
wrote:
> Can you give a simple example of what you''re trying to do?
It''s much
> easier discussing specifics.
Sorry - I somehow managed to miss your post which gave the example.

Hi Paul,

Are you able to expand upon your actual requirements?  I''ve just been
speaking to James (mocha author) and we''re pretty certain we can help
but would like a little more clarification.

Cheers,

Chris

On 8/15/06, James Mead <jamesmead44@gmail.com>
wrote:
> On 14/08/06, James Mead <jamesmead44@gmail.com> wrote:
> > Can you give a simple example of what you''re trying to do?
It''s much
> > easier discussing specifics.
>
> Sorry - I somehow managed to miss your post which gave the example.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

Chris Roos wrote:
> Are you able to expand upon your actual requirements?  I''ve just
been
> speaking to James (mocha author) and we''re pretty certain we can
help
> but would like a little more clarification.
Hi Chris,

Apologies for the delayed reply - I use ruby-forum.com to keep up with 
this list, and it seems to have been a bit "wobbly" recently :-(

Rather than concoct another example, I''ll give you a simplified version
of our actual code. Our system sends and receives (SMS) messages. We 
have a Conversation model class which represents a set of incoming and 
outgoing messages. One of the methods on Conversation is 
"send_unsolicited" which creates a Conversation containing a single 
outgoing message and then sends the message. The code goes something 
like this:

class Conversation
  class << self
    def send_unsolicited(customer, message)
      c = create_unsolicited(customer, message)
      c.send_now!
      c.unlock!
      return c
    end

    def create_unsolicited(customer, message)
      c = Conversation.create :customer => customer, :locked_by_user_id 
=> 1
      m = c.create_in_progress_outgoing_message :body => message
      return c
    end
  end

  def unlock!
    self.locked_by_user = nil
    save!
  end

  def create_in_progress_outgoing_message(options = {})
    # ...
  end

  def send_now!
    # ...
  end
end

We have a test in which, among other things, we want to verify that 
send_unsolicited unlocks the conversation. It''s not enough for us to 
verify that the conversation isn''t locked when it returns - we need to 
be certain that it''s actually called the unlock! method.

At the moment the test is as follows:

module HookCreate
  def new(options = {})
    c = super options
    c.extend HookUnlock
    return c
  end
end

module HookUnlock
  attr_reader :was_unlocked

  def unlock!
    super
    @was_unlocked = true
  end
end

def test_send_unsolicited
  Conversation.extend HookCreate

  c = Conversation.send_unsolicited customers(:customer1), "Blah blah 
blah"
  assert c.was_unlocked
end

Which works, but is nasty. And doesn''t scale well if more than one test
needs to do the same thing.

Make sense?

Ideally, we would like some way to say "in the test environment, 
whenever you create a Conversation class, instrument it as follows". The 
test/mocks directory gives us a convenient way of saying "in the test 
environment, whenever you create a Conversation class, create this mock 
class instead", but that''s not quite what we want :-(

If a mock could extend the class that it''s pretending to be instead of 
simply replacing it, that would be perfect. But I''m not aware of any
way
to achieve this in Rails as things stand.

Thanks in advance for your help!

paul.butcher->msgCount++

-- 
Posted via http://www.ruby-forum.com/.

On 15/08/06, Paul Butcher <paul@paulbutcher.com>
wrote:
> Rather than concoct another example, I''ll give you a simplified
version
> of our actual code. Our system sends and receives (SMS) messages. We
> have a Conversation model class which represents a set of incoming and
> outgoing messages. One of the methods on Conversation is
> "send_unsolicited" which creates a Conversation containing a
single
> outgoing message and then sends the message. The code goes something
> like this:
>
> class Conversation
>   class << self
>     def send_unsolicited(customer, message)
>       c = create_unsolicited(customer, message)
>       c.send_now!
>       c.unlock!
>       return c
>     end
>
>     def create_unsolicited(customer, message)
>       c = Conversation.create :customer => customer, :locked_by_user_id
> => 1
>       m = c.create_in_progress_outgoing_message :body => message
>       return c
>     end
>   end
>
>   def unlock!
>     self.locked_by_user = nil
>     save!
>   end
>
>   def create_in_progress_outgoing_message(options = {})
>     # ...
>   end
>
>   def send_now!
>     # ...
>   end
> end
>
> We have a test in which, among other things, we want to verify that
> send_unsolicited unlocks the conversation. It''s not enough for us
to
> verify that the conversation isn''t locked when it returns - we
need to
> be certain that it''s actually called the unlock! method.
>
> At the moment the test is as follows:
>
> module HookCreate
>   def new(options = {})
>     c = super options
>     c.extend HookUnlock
>     return c
>   end
> end
>
> module HookUnlock
>   attr_reader :was_unlocked
>
>   def unlock!
>     super
>     @was_unlocked = true
>   end
> end
>
> def test_send_unsolicited
>   Conversation.extend HookCreate
>
>   c = Conversation.send_unsolicited customers(:customer1), "Blah blah
> blah"
>   assert c.was_unlocked
> end
>
> Which works, but is nasty. And doesn''t scale well if more than one
test
> needs to do the same thing.
>
> Make sense?
>
> Ideally, we would like some way to say "in the test environment,
> whenever you create a Conversation class, instrument it as follows".
The
> test/mocks directory gives us a convenient way of saying "in the test
> environment, whenever you create a Conversation class, create this mock
> class instead", but that''s not quite what we want :-(
>
> If a mock could extend the class that it''s pretending to be
instead of
> simply replacing it, that would be perfect. But I''m not aware of
any way
> to achieve this in Rails as things stand.
>
> Thanks in advance for your help!
Hi Paul,

You could use Mocha to do the following...

def test_send_unsolicited
  conversation = mock()
  conversation.stubs(:send_now!)
  conversation.expects(:unlock!)
  Conversation.stubs(:create_unsolicited).returns(conversation)
  Conversation.send_unsolicited(nil, nil)
end

Mocha will auto-verify the expectation that Conversation#unlock! is
called at the end of the test_send_unsolicited method (in a secret
teardown). You no longer need any of the Hook modules. Note that all
stubbed/expected methods will not execute their normal
implementations, however the class will be put back to normal after
the test_send_unsolicited method ends. This test is stubbing out a lot
of code, but it is focussed on verifying the unlock! call. An
alternative is...

def test_send_unsolicited
  Conversation.any_instance.expects(:unlock!)
  Conversation.send_unsolicited(customers(:customer1), "Blah blah
blah")
  Conversation.any_instance.verify
end

This only replaces the unlock! method and verifies that it was called,
so in this case you need to supply the parameters to send_unsolicited,
so that create_unsolicited has something to work with. In this case,
with the current version of Mocha, you need to manually call verify.

I''m afraid I haven''t had time to check this works, but I think
it should be ok.

Make any sense?

James.
http://blog.floehopper.org

James Mead wrote:
> You could use Mocha to do the following...
> 
> def test_send_unsolicited
>   conversation = mock()
>   conversation.stubs(:send_now!)
>   conversation.expects(:unlock!)
>   Conversation.stubs(:create_unsolicited).returns(conversation)
>   Conversation.send_unsolicited(nil, nil)
> end
> 
> ... This test is stubbing out a lot
> of code, but it is focussed on verifying the unlock! call.
Which means that we can''t use this approach in our particular case - 
although the only thing that the example I gave you does is verify that 
unlock! is called, the "real" test does quite a bit more :-)

However:
> An alternative is...
> 
> def test_send_unsolicited
>   Conversation.any_instance.expects(:unlock!)
>   Conversation.send_unsolicited(customers(:customer1), "Blah blah
blah")
>   Conversation.any_instance.verify
> end
> 
> This only replaces the unlock! method and verifies that it was called,
> so in this case you need to supply the parameters to send_unsolicited,
> so that create_unsolicited has something to work with. In this case,
> with the current version of Mocha, you need to manually call verify.
I think that this gives us exactly what we want :-)

Thank you!
> Make any sense?
Perfect sense. I''m installing Mocha now... :-)

Cheers!

paul.butcher->msgCount++

-- 
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On 16/08/06, Paul Butcher <paul@paulbutcher.com>
wrote:
>
> Perfect sense. I''m installing Mocha now... :-)

Great! I''d welcome any feedback.

James.
http://blog.floehopper.org
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---------- Forwarded message ----------
From: Paul Butcher <paul at paulbutcher.com>
Date: 16-Aug-2006 12:55
Subject: [Rails] Re: Re: Re: A mock which extends rather than replaces a
clas
To: rails at lists.rubyonrails.org

James Mead wrote:
> You could use Mocha to do the following...
>
> def test_send_unsolicited
>   conversation = mock()
>   conversation.stubs(:send_now!)
>   conversation.expects(:unlock!)
>   Conversation.stubs(:create_unsolicited).returns(conversation)
>   Conversation.send_unsolicited(nil, nil)
> end
>
> ... This test is stubbing out a lot
> of code, but it is focussed on verifying the unlock! call.
Which means that we can''t use this approach in our particular case -
although the only thing that the example I gave you does is verify that
unlock! is called, the "real" test does quite a bit more :-)

However:
> An alternative is...
>
> def test_send_unsolicited
>   Conversation.any_instance.expects(:unlock!)
>   Conversation.send_unsolicited(customers(:customer1), "Blah blah
blah")
>   Conversation.any_instance.verify
> end
>
> This only replaces the unlock! method and verifies that it was called,
> so in this case you need to supply the parameters to send_unsolicited,
> so that create_unsolicited has something to work with. In this case,
> with the current version of Mocha, you need to manually call verify.
I think that this gives us exactly what we want :-)

Thank you!
> Make any sense?
Perfect sense. I''m installing Mocha now... :-)

Cheers!

paul.butcher->msgCount++

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