[rspec-users] [Q] testing WIN32OLE_EVENT callbacks

Chuck Remes
Thu, 27 Aug 2009 16:02:26 -0000

On Aug 27, 2009, at 10:12 AM, Matt Wynne wrote:

>
> On 26 Aug 2009, at 19:57, Chuck Remes wrote:
>
>> I''m trying to setup some specs (really just assertions) that
verify
>> some callbacks are executed in response to COM events. In the
>> WIN32OLE_EVENT class you may subscribe to a COM event and have it
>> delivered to you for processing. Syntax looks like:
>>
>>             event_handler.on_event(''StartEvent'') do
|*args|
>>               do_start_event args
>>             end
>>
>> The #do_start_event method is a member of the containing class. The
>> only way I can confirm that it is being called is to set an
>> expectation on the class under test. I''ve always noted that
mocking/
>> stubbing the class under test is rather bad form. Regardless, I
>> don''t know how to "mock" the delivery of an event
anyway so this
>> may all be moot.
>>
>> I searched the list archives for ''win32ole'' back to
early 2007 and
>> came up with 0 hits. Any suggestions on how to tackle this?
>
> This doesn''t really have much to do with the specific technology
> you''re dealing with, it''s an issue about separating the
layers so
> you can introduce fakes where you need to in order to test your own
> code.
>
> Can you use dependency injection (or some other trick) to swap in a
> fake event_handler into the code you''ve quoted above? If so, you
can
> then get your fake to simulate the behaviour of the event_handler
> and exercise the code you want to actually test.
>
> There are a couple of good books on these sort of techniques:
> http://xunitpatterns.com/
>
http://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052
>
> does that help?

It does somewhat. I will definitely be looking at that XUnit patterns
book.

To answer an earlier question, I *can* pass in a mock for
event_handler. However, I fail to see how I can use that in the
example above to test that the statements in the block are executed.

def bar event_handler
   event_handler.on_event(''StartEvent'') do |baz, qux|
     @obj1.method1 baz, qux
   end
end

Let''s assume that method1 and method2 are acting upon other objects
that I can also mock via DI. How can I generate the
''StartEvent'' so
that the block above is executed? BTW, the layers are as separated as
they are going to get. In the WIN32OLE_EVENT class you *must* pass a
block as shown above. I don''t know how to get that block to execute in
my specs without actually connecting to the COM service and getting it
to generate that ''StartEvent''. Do you know of another way?

it "should execute the block upon receipt of event
''StartEvent''" do
   handler = mock("event handler")
   handler.should_receive(:on_event).with(''StartEvent'') #
necessary?

   obj1_mock = mock("obj1")
   obj1.should_receive(:method1)

   foo = Foo.new
   foo.obj1 = obj1

   foo.bar
   # callback has been set; how do I generate the ''StartEvent''
   # to run that block?
   foo.???
end

Do you see my problem more clearly with this example? Or have I
obfuscated it even more... :)

cr