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
following:
mock_engine = mock("Engine")
mock_engine.should_receive(:ignite)
car = Car.new(mock_engine)
car.start
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
good.
Now, here's what I don't understand: suppose I refactor the Engine
class
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.
Scott
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