[rspec-users] Mocks and Refactoring - doing it wrong?
mailing_lists at railsnewbie.com
Thu Oct 30 01:26:01 EDT 2008
On Oct 30, 2008, at 1:02 AM, Sebastian W. wrote:
> Hello RSpec folks,
> I've only been introduced to the world of mock objects since Wednesday
> of last week, so go easy on me if I come off as ignorant. :P
> So, I'm a big fan of testing, especially since it has really helped to
> do refactoring in the past. But, I'm running into an issue that I'm
> hoping could be cleared up. Let's say that I have some code like the
> mock_engine = mock("Engine")
> car = Car.new(mock_engine)
> Internally, the car class calls "ignite" on the engine that was passed
> to the constructor. We run the spec, everything is green. So far, so
> Now, here's what I don't understand: suppose I refactor the Engine
> and rename the "ignite" method to "turn_on". If I re-run the example
> from above, the test is still green - but it shouldn't be, since the
> "ignite" method doesn't exist on the Engine class anymore.
> So I'm wondering...what am I doing wrong? I feel like my tests should
> help catch these sorts of things when I do a refactoring - my hunch is
> that I'm missing a step here.
The step your missing is that using mocks is different then classical,
black box testing.
When you use a mock object, you're making a tradeoff. One of the
things you gain is isolation. For instance, if you were testing a
webservice or a database, you may not care about it being around *for
this test*. Another thing you're gaining is pure speed (of the
running test case) - you simply won't have to go through the full
stack. On the other hand, that's also what your loosing - meaning
that if that API changes, your screwed.
This is why anyone who knows anything about testing will recommend
several different layers of tests - some very close to the metal which
will use mocks (which can be repeatedly run quickly), and others which
are closer on the integration side of the spectrum.
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