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Subject: Re: [boost] Preferred way to simulate system calls
From: Jonathan Biggar (jon_at_[hidden])
Date: 2017-11-06 23:07:36

A better way than virtual is to make the code you want to test into a
template that takes a class parameter that provides the functions you want
to mock. It's easy to make it testable while sacrificing no performance.

On Nov 6, 2017 14:57, "Andrey Semashev via Boost" <boost_at_[hidden]>

> On 11/07/17 01:00, James E. King, III via Boost wrote:
>> I like to test every branch, and I have a class that calls
>> open/read/close. It uses a hardcoded filename ("/dev/urandom"). It is a
>> template in a detail namespace. What's the "boost way" when it comes to
>> mocking these system calls? Should I make protected methods that normally
>> call open/read/close, then subclass in a test and override them with
>> different logic to force error paths?
> I'm not aware of any mocking support in Boost. But I would be opposed if,
> for the sake of testing, you would mangle the code so that functionality or
> performance is affected. I.e. what you describe would require these methods
> to be virtual, which is absolutely useless and harmful in normal use.
> I guess, if you really want to test you're actually calling
> open/read/close, you could build a mocking library and use LD_PRELOAD to
> inject it into the test. Or you could implement those functions in the test
> itself, so that they are resolved to by the linker. Unfortunately, I'm
> afraid you will have to deal with platform-specific linker API to forward
> unrelated calls to the real open/read/close functions.
> I don't think it is necessary to do a this deep test though. If you can
> reasonably test that the generation works as expected (i.e. 10 calls return
> 10 different conforming UUIDs), that would be enough. If you can test the
> generator by replacing the random_device used in the test, that's great.
> Just don't add any unnecessary overhead for that and don't make it easy to
> use the test code in real code by accident.
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