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Subject: Re: [Boost-users] Recommended mock framework to use with Boost?
From: Mathieu Champlon (mathieu.champlon_at_[hidden])
Date: 2012-01-19 20:02:03

On 17/01/2012 16:18, Chris Cleeland wrote:
> (...)
> What I found in my situation, though, was that mocking took a
> substantial amount of development effort in a "legacy"(*) body of code
> such that creating tests that rely upon mocking was more trouble than
> it was worth at first evaluation, i.e., it did not save me more time
> than it cost. As this was my first experience with an actual mocking
> framework (as opposed to ad-hoc bespoke stuff created for a single
> purpose), I'm not sure if it's a framework issue, a user (me) issue,
> an impedance mismatch between the framework and legacy code, or what.
> I suspect that the reality is that it's a little of all of them.
> If anybody knows a mocking framework that slides easily into existing,
> and sometimes grungy (from a TDD perspective), code base, I'd love to
> hear about it.
> (*) By "legacy" I mean code that was not written with a test-driven
> development mindset.
Hi Chris,

I don't have the answer to your question but if your legacy code was
developed with "traditional" unit tests, or even without tests, it isn't
going to be easy to introduce mock objects because it actually means
turning everything upside-down.
Using mock objects tends to drive the code to be more "push" (ask others
to do things) and less "pull" (collect data in order to do things) than
the usual. Most of the test cases don't even check any results in the
end, they just expect calls.
It's not just a convenient way of faking components in order to test
them more easily, it's also a way of driving the code a bit differently.

 From my experience, trying to use mock objects after a component has
been written results in lengthy test cases which need to configure many
mock objects and/or many expectations in order to work.
I have seen for instance tests like this :

     some_mock a;
     MOCK_EXPECT( a.get_some_data ).once().with( -100.f, 100.f
).returns( 0 );
     MOCK_EXPECT( a.get_some_data ).once().with( 0.f, 100.f
).returns( 1 );
     MOCK_EXPECT( a.get_some_data ).once().with( 100.f, 100.f
).returns( -1 );
     // etc... for A LOT of lines
     some_class b( a );
     b.do_something( 12, 42, 77 );
     BOOST_CHECK_EQUAL( 654, b.result() );

This is indeed cumbersome to write and hard to maintain, and to someone
accustomed to TDD it's a smell this most likely wasn't. :)
My usual approach is either scrap the component and start from scratch,
or just leave it be if it doesn't impact much the rest of the system...


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