Unit tests and segfaults

[Jonathan M Davis]

On Thursday, December 06, 2012 09:02:29 Russel Winder wrote:
> What is the right idiom for testing that a function call does segfault
> when you want it to?

Why would you _want_ a function to segfault? That's like asking how to write a 
function which tests that a computer is off after you pull the plug.

Regardless, since segfaults pretty much just kill the program, I don't think 
that you can do much. You could install a signal handler to catch the 
segfault, but segfaults aren't exceptions, and AFAIK, it's not possible to 
continue the program (or at least that thread) in any meaningful way at that 
point. It's also the case that the signal handler is completely separate from 
the function being called or the code which is testing that function, making 
it so that you can't continue the execution of your test code, and you have no 
way of really knowing whether than segfault came from where you wanted it to. 
You could set a variable before the function and unset it afterwards so that 
the signal handler could test its state (with the idea that if that variable 
has been set, the segfault came from that code), but if any other threads are 
running, _they_ could have caused any segfaults which occur (regardless of the 
state of that variable), and even if you have only one thread, there's no way 
to know that the segfault was generated from the exact spot that you intended 
rather than a stray null pointer or whatnot in the code being tested.

- Jonathan M Davis