[rspec-users] Post call verification

David Chelimsky dchelimsky at gmail.com
Wed Mar 23 14:59:39 EDT 2011


[moved your post to the bottom for consistency with this thread]

On Mar 23, 2011, at 1:41 PM, Srushti wrote:

> On 22 March 2011 17:22, <rspec-users-request at rubyforge.org> wrote:
> 
> Date: Tue, 22 Mar 2011 06:52:02 -0500
> From: David Chelimsky <dchelimsky at gmail.com>
> To: rspec-users <rspec-users at rubyforge.org>
> Subject: Re: [rspec-users] Post call verification
> Message-ID: <3237C672-2BB7-446C-9AE5-E25447CE25C8 at gmail.com>
> Content-Type: text/plain; charset="us-ascii"
> 
> On Mar 22, 2011, at 4:13 AM, Tom Stuart wrote:
> 
> > On 19 Mar 2011, at 13:35, David Chelimsky wrote:
> >
> >> On Mar 18, 2011, at 10:37 AM, Srushti Ambekallu wrote:
> >>
> >>> Hey all,
> >>>
> >>> I would like to be able to be able to have mocks where I can make all the calls and assert that it was called afterwards. This would be especially useful when asserting on a doing-method whose return value is not being considered.
> >>> e.g.
> >>> service = mock(ExternalService)
> >>> ExternalService.stub!(:new).and_return(service)
> >>> user = User.new
> >>> user.activate
> >>> service.should_have_received(:publish_user_activation).with(user)
> >>> Now this obviously can't replace all assertions done with should_receive, but I know there are at least a few cases where this would come in handy and be more readable. I know while writing tests, I usually write the actual call (in this case the 'post') and then go up a couple of lines to write the should_receive. I think it would be more natural to verify it after the fact rather than before. I seem to remember there was another mocking library which     did something quite close to this, but I just can't seem to find it just now. What does everyone think? I could try and implement this myself, but just wanted to see if there was any interest, or any one had a good reason not to include this.
> >>
> >> This pattern is called a test spy, and there has been much discussion of it on this list:
> >>
> >> http://groups.google.com/group/rspec/search?group=rspec&q=test+spies&qt_g=Search+this+group
> >>
> >> The biggest issue for me is that message expectations often get set with a stub return value:
> >>
> >>   foo.should_receive(:bar).and_return(:baz)
> >>   foo(:bar)
> >>
> >> In a world of test spies, this would be:
> >>
> >>   foo.stub(:bar).and_return(:baz)
> >>   foo(:bar)
> >>   foo.should_have_received(:bar).with(:bam)
> >>
> >> This requires more code in the example, and creates an otherwise unnecessary binding between the stub and the expectation. Also, note that the stub doesn't constrain the argument to bar(), but should_have_received() does (in this example). If we were to do that the other way:
> >>
> >>   foo.stub(:bar).with(:baz).and_return(:bam)
> >>   bar(:something_other_than_baz)
> >>   foo.should_have_received(:bar)
> >>
> >> ... should this pass or fail? As rspec-mocks works today, it could only pass if we had an additional stub at the beginning.
> >>
> >>   foo.stub(:bar)
> >>   foo.stub(:bar).with(:baz).and_return(:bam)
> >>   bar(:something_other_than_baz)
> >>   foo.should_have_received(:bar)
> >>
> >> ... because calling bar(:anything_other_than_baz) would not work due to the with() constraint.
> >>
> >> If we agree it should fail, then that's pretty confusing as well, since foo did actually receive bar() and the only way to understand to failure is to look back at the stub with the with() constraint.
> >>
> >> I could go on but I think this makes the point. We don't have test spies in RSpec yet because a) I don't personally find them valuable and b) they introduce more problems than they solve.
> >>
> >> That said, if anyone cares to write an external library to support this, I'd gladly work with you to make sure RSpec provides you the extension points you need.
> >>
> >> Cheers,
> >> David
> >> _______________________________________________
> >> rspec-users mailing list
> >> rspec-users at rubyforge.org
> >> http://rubyforge.org/mailman/listinfo/rspec-users
> >
> > This is a long-running discussion and I suspect it comes down to personal preference in the end more than anything else. However, I have done some work to get a basic test spy library working with rspec which tries to avoid unnecessary stubbing to allow assertion on method calls (i.e. you only need to set up a stub as well when you need to manipulate the return value). It's in its infant stages and needs some TLC (in particular, its factory method 'spy' is in the global namespace, when it could and should be dealt with more elegantly), but it may be of some use for test spy fanatics... https://github.com/mortice/matahari
> 
> Thanks, Tom. Let me know if there is anything you need in RSpec to make it easy to plug this in.
> 



> If anyone is interested, I wrote a quick little gem to add spies to rspec-mocks. Basically, it adds a method called spy which internally returns a mock.as_null_object, and a matcher for "have_received(:method)" & "have_received(:method).with(args)".
> David, my understanding of your point (or at least, part of it) is that you'd rather use mocks since they fail on the method calls that have never been set up.

That's not what I said. Please re-read my examples above - they are about the cases where a stubbed return value matters for the code to run, which happens much more often than it would if we all followed Tell, Don't Ask (but we don't so much).

> The way I see it, if I want something to fail I'd rather make it explicit. I'd rather explicitly state that "object.should_not have_received(:wrong_method)" so that the test is perfectly clear, than want to use a standard mock which would fail . This is the same reason I imagine we have "lambda {a_call}.should_not raise_error". We don't really need that since the test fails because of an exception nonetheless. Of course, mocks would also work as a general check against calls to other methods.
> The last time I used something like this (when using RhinoMocks working on a .net project) if you had to have a return (that your production code would use) you would set up the expectation before hand with a :should_receive. You would only use the :have_received matcher on calls that you didn't need to set an expectation on. Even though this might be seem to be a little consistent, with a little of this and a little of that, it worked out quite well on us, with the added benefit of not needing stubs on methods where the return value doesn't matter and you saving a little bit of noise in your tests.
> Nonetheless, here's the gem: http://rubygems.org/gems/stirlitz
> Thanks,
> Srushti
> 



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