[swift-evolution] Solving the issue of unit-testing precondition with the Standard Library?

[Step C]

I think the forking approach is correct and would like to see more tooling support for that path in test runners. 

> On Mar 13, 2016, at 5:20 AM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Okay, perhaps this is not the optimal solution. But I tried to rally enthusiasm for finding a solution using forks a few months back and the complexity of the problem seemed to stall the progress. The issue is important enough for me that I tried to come at it from a different angle. If be more than happy if it was implemented using forks.
> 
>> On 13 Mar 2016, at 01:28, Jonathan Tang <jonathan.d.tang at gmail.com> wrote:
>> 
>> 
>> 
>>> On Sat, Mar 12, 2016 at 1:41 PM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
>>> I am deeply interested in finding solutions for allowing unit-tests of preconditions. Without them, I believe we are leaving many holes in our tests and coverage. The solution found in the Swift project of forking the process seems fairly complicated to implement in XCTest.
>>> 
>>> I found a solution online that works by overriding the precondition function with a function that calls a configurable closure which defaults to the original precondition function. It would be great if the Standard Library allowed this by default so that XCTest could use it to offer full support for precondition unit tests.
>>> 
>>> http://stackoverflow.com/a/31349339
>>> 
>>> Is this imaginable?
>> 
>> +1 to this being an important problem to solve, but I'm not sure about the specific solution.  Are there performance or security impacts to production code by having this?  Could the forked-process solution be implemented once in a framework and then everybody just uses it transparently?  The forked-process approach also has the advantage of catching crashes for any other unexpected reason (eg. division by zero), and of ensuring that test executions are hermetically sealed without data leaking between test instances.
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