parallel doing - for tests

do_parallel.js

function doParallelNTimes(n,concurrent,fn,cb) {
    var outstanding = 0;
    var complete = 0;
    var nth = 0;

    times(Math.min(concurrent,n),loop);

    function loop() {
        if(outstanding >= concurrent)  {
            return;
        }
        outstanding += 1;
        fn(nth,function(err,nth) {
            outstanding -= 1;
            complete += 1;
            if(err) {
                return cb(err);
            }
            if(complete === n) {
                cb();
            } else {
                var totalLeft = n - (complete + outstanding);
                var unusedConcurrency = concurrent - outstanding;
                var toLoop = Math.max(0,totalLeft < unusedConcurrency ? totalLeft : unusedConcurrency);
                times(toLoop,loop);
            }
        });
        nth += 1;
    }
}

function times(n,fn) {
    while(n--) fn();
}