A test like that isn't guaranteed to fail. It depends on the hardware, the maiden name of your mother, as well as the position of the moon :)

I don't mind having tests like that in the test suite, as long as the test writer saw them fail ([seeing the test fail is important](http://blog.ploeh.dk/2013/04/02/why-trust-tests)), because, while we aren't guaranteed that they always failed, once the implementation is correct, it must *never* fail.

If you can get it to fail semi-reliably on your machine, it would be great to add such a test. If not, then don't bother with it, but please still add some thread-safety.