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

[Dmitri Gribenko]

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?

What would precondition() if the condition evaluates to false, and the
special handler is installed?  precondition() can't return, since it
can't allow the original code to continue.  The original code
certainly does not expect to continue (it can even do something
memory-unsafe, or force-unwrap an nil optional, or advance an index
past endIndex, etc.)

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/