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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