rspec users - Nov 2011 - Weird behavior with should_not_receive

I recently saw a test passing when it should have failed, because the
person who wrote it used should_not_receive instead of
should_receive.  Here is a simple example illustrating the behavior:

class MyTest
  def foo
    puts "hey"
  end

  def bar
    foo
  end
end

describe MyTest do
  it "passes but should fail" do
    subject.should_not_receive(:foo).once
    subject.bar
  end
end

If I remove the ".once" the test fails, as I would expect.

Is this intended behavior?  It seems really weird to me.

I am seeing this with rspec 1.3.2 and rspec-rails 1.3.4.

Thanks,
David

On Nov 1, 2011, at 12:59 PM, David Hofer wrote:
> I recently saw a test passing when it should have failed, because the
> person who wrote it used should_not_receive instead of
> should_receive.  Here is a simple example illustrating the behavior:
> 
> class MyTest
>  def foo
>    puts "hey"
>  end
> 
>  def bar
>    foo
>  end
> end
> 
> describe MyTest do
>  it "passes but should fail" do
>    subject.should_not_receive(:foo).once
>    subject.bar
>  end
> end
> 
> If I remove the ".once" the test fails, as I would expect.
> 
> Is this intended behavior?  It seems really weird to me.
> 
> I am seeing this with rspec 1.3.2 and rspec-rails 1.3.4.
It is really weird, but it''s also a misunderstanding of the API.

should_receive(:foo) defaults to an expectation of 1 time. The object then
exposes methods like once, twice, exactly(3).times to specify/modify the
expectation:

    foo.should_receive(:bar).once
    foo.should_receive(:bar).twice
    foo.should_receive(:bar).exactly(3).times

Yes, I was sorely tempted to support foo.should_receive(:bar).three_times_a_lady
when we added all that, but I refrained. Now that Siri will reenact the entire
"Who''s on first?" routine, I''m reconsidering.

That aside, to specify that a message would not be received, we used to have to
write:

    foo.should_receive(:bar).exactly(0).times

We later added foo.should_not_receive(:bar) as a shorter, more expressive
version of that.

So, since methods like once, twice, exactly(n).times, at_least(n).times and
at_most(n).times all modify the constraint, it turns out that they could be used
together, like this:

    foo.should_receive(:bar).once.twice.exactly(3).times

In this case, it would expect :bar 3 times, because the last modification wins.

Of course you would never do that deliberately, and in my 5 1/2 years running
this project this is the first time I''ve ever seen any issue w/ this,
but that is actually not prevented. Therefore, the following are equivalent:

    foo.should_receive(:bar).exactly(0).times.once
    foo.should_not_receive(:bar).once

Hope that helps you to understand the problem. In terms of what we can/will do
about it, I don''t really think we''ll do anything about it but
document it better. It would require too much work to solve this without
breaking other things, and it turns out that mocha, flexmock, and RR all have
the same issue:

    foo.expects(:bar).never.once
    flexmock(foo).should_receive(:bar).never.once
    mock(foo).bar.never.once

Cheers,
David

Double negatives are not unconfusing.

Not unlike chaining mutable decorator objects.

(I was tempted to say "non-immutable" but that would chain the jokes)

btw with .once and .twice, why not .thrice? Lady or no.

-- 
Alex Chaffee - alex at stinky.com
http://alexchaffee.com
http://twitter.com/alexch
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On Nov 6, 2011, at 4:45 PM, Alex Chaffee wrote:
> Double negatives are not unconfusing.
> 
> Not unlike chaining mutable decorator objects.
> 
> (I was tempted to say "non-immutable" but that would chain the
jokes)
> 
> btw with .once and .twice, why not .thrice? Lady or no.
module Thrice
  def thrice(&block)
    exactly(3).times &block
  end
end

RSpec::Mocks::MessageExpectation.send :include, Thrice

There you go :)

On Sun, Nov 6, 2011 at 2:55 PM, David Chelimsky <dchelimsky at
gmail.com>wrote:
> There you go :)
>
You are three times a gentleman, David.

-- 
Alex Chaffee - alex at stinky.com
http://alexchaffee.com
http://twitter.com/alexch
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