[rspec-users] Post call verification

Tom Stuart tom at therye.org
Tue Mar 22 05:13:42 EDT 2011


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
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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

Cheers,

Tom

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