"make std/concurrency.test" fails but others don't... why?

[Vladimir Panteleev via Digitalmars-d]

On Friday, 10 April 2015 at 23:04:44 UTC, Andrei Alexandrescu 
wrote:
> Martin Nowak added recently a nice feature to the Phobos 
> makefile: by specifying e.g.
>
> make std/stdio.test
>
> only the unittests for std/stdio.d would build and run. This 
> greatly improves development turnaround for Phobos.

FWIW, in most cases you can also do this simply by running:

dmd -unittest -main -run stdio.d

It won't work if other modules have changed (compared to the dmd 
in your PATH).