[rspec-users] how to write spec for infinite loop?

[zuo peng]

Hi,

I've got trouble when describe infinite loop.

code snippet:

def start_loop
while true
data = self.server.handle_client
if data
self.manager.dispatch(data)
end
end
end

without the loop, it is easy to test the logic.
but how can I describe it to tell the developer ( me :-) ) that there
should be an infinite loop inside.
thanks.

Regards,

Peng Zuo
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[Edvard Majakari]

On Thu, May 29, 2008 at 9:25 AM, zuo peng <cn.pe...@gmail.com> wrote:

> Hi,
>
> I've got trouble when describe infinite loop.
>
> code snippet:
>
> def start_loop
> while true

Not a reply to your specific question, but hopefully even better.

I stumbled into similar situation a while ago, when I was developing a
daemon process using BDD.
When writing the test, I came up naturally with the following kind of structure:

def start_loop
while loop_condition?
do_the_magic
end
end

the idea is to separate looping logic and the operations done inside.
The whole method start_loop was very easy to test now:

MyDaemon.stub!(:loop_condition?).and_return(true, false) # I didn't
use RSpec at the time, so this might not work
...
outcome.should be_something_expected

The trick is in stubbing the class/module method loop_condition? so
that it returns true the first time and false the second time,
thus looping only once. In the actual implementation loop_condition?
was implemented as follows:

class MyDaemon
def loop_condition?; true; end
...
end

thus making the while loop indefinite.

Any smart developer could have come up with similar structure without
using TDD/BDD. However, that particular solution came to me
naturally exactly because of the way BDD works: it forces you -- in a
tender way -- to write code that is easy to test automatically.

--
"One day, when he was naughty, Mr Bunnsy looked over the hedge into
Farmer Fred's field and it was full of fresh green lettuces. Mr
Bunnsy, however, was not full of lettuces. This did not seem fair."
-- Terry Pratchett, Mr. Bunnsy Has An Adventure

[Scott Taylor]

On May 29, 2008, at 2:25 AM, zuo peng wrote:

> Hi,
>
> I've got trouble when describe infinite loop.
>
> code snippet:
>
> def start_loop
> while true
> data = self.server.handle_client
> if data
> self.manager.dispatch(data)
> end
> end
> end
>
> without the loop, it is easy to test the logic.
> but how can I describe it to tell the developer ( me :-) ) that there
> should be an infinite loop inside.

Here's a tip which Aslak gave me several months ago, and I find myself
repeating it in many different contexts on this mailing list:

One way is with dependency injection:

def start_loop(looping_infinitely = true)
while looping_infinitely
...
end
end

In your spec, you simply pass false (but production code can call the
method as if there is no option).

Scott

[David Chelimsky]

On May 29, 2008, at 12:31 AM, Scott Taylor wrote:

>
> On May 29, 2008, at 2:25 AM, zuo peng wrote:
>
>> Hi,
>>
>> I've got trouble when describe infinite loop.
>>
>> code snippet:
>>
>> def start_loop
>> while true
>> data = self.server.handle_client
>> if data
>> self.manager.dispatch(data)
>> end
>> end
>> end
>>
>> without the loop, it is easy to test the logic.
>> but how can I describe it to tell the developer ( me :-) ) that there
>> should be an infinite loop inside.
>
> Here's a tip which Aslak gave me several months ago, and I find
> myself repeating it in many different contexts on this mailing list:
>
> One way is with dependency injection:
>
> def start_loop(looping_infinitely = true)

:)

I think calling this dependency injection is a bit of a stretch. I
agree with the approach of having a logical default that you can
override in the example, but what exactly is the dependency on? true?

Regardless of its name, this is a very good solution to the problem at
hand.

[Scott Taylor]

Yeah, good point. It makes me laugh a bit too, now that I think about
it.

Also, shouldn't the dependency occur in the constructor for it to be
real DI?

[zuo peng]

Thanks guys.
Both ways work perfectly.

Regards,

Peng Zuo

[Pat Maddox]

If ever there were a time to drop Ruby and start using Java + Guice,
this would be it.

Pat

[Kero]

>> I've got trouble when describe infinite loop.
>>
>> code snippet:
>>
>> def start_loop
>> while true
>> data = self.server.handle_client
>> if data
>> self.manager.dispatch(data)
>> end
>> end
>> end
>>
>> without the loop, it is easy to test the logic.
>> but how can I describe it to tell the developer ( me :-) ) that there
>> should be an infinite loop inside.
>
> Here's a tip which Aslak gave me several months ago, and I find myself
> repeating it in many different contexts on this mailing list:
>
> One way is with dependency injection:
>
> def start_loop(looping_infinitely = true)
> while looping_infinitely
> ...
> end
> end
>
> In your spec, you simply pass false (but production code can call the
> method as if there is no option).

"while true" is also known as "loop" in Ruby.
Really, you do not want to test whether that ruby construct works, do you?
(I can imagine it being in the test suite that is for RUby itself)

What I think is interesting for you to test, is that your loop keeps running
when the dispatcher dies, and possibly other bad-weather cases. I bet your
loop is in another Thread, and checking whether a Thread still runs is easy
enough (also interesting enough, since threads die by themselves in Ruby,
by default, i.e. they do not raise exceptions in other threads unless you
set Thread.abort_on_exception = true).