function doDuring(fn, test, callback) {
    callback = onlyOnce(callback || noop);

    var next = rest(function (err, args) {
        if (err) return callback(err);
        args.push(check);
        test.apply(this, args);
    });

    function check(err, truth) {
        if (err) return callback(err);
        if (!truth) return callback(null);
        fn(next);
    }

    check(null, true);
}
The post-check version of [`during`]{@link module:ControlFlow.during}. To reflect the difference in
the order of operations, the arguments `test` and `fn` are switched.

Also a version of [`doWhilst`]{@link module:ControlFlow.doWhilst} with asynchronous `test` function.
@name doDuring
@static
@memberOf module:ControlFlow
@method
@see [async.during]{@link module:ControlFlow.during}
@category Control Flow
@param {Function} fn - A function which is called each time `test` passes.
The function is passed a `callback(err)`, which must be called once it has
completed with an optional `err` argument. Invoked with (callback).
@param {Function} test - asynchronous truth test to perform before each
execution of `fn`. Invoked with (...args, callback), where `...args` are the
non-error args from the previous callback of `fn`.
@param {Function} [callback] - A callback which is called after the test
function has failed and repeated execution of `fn` has stopped. `callback`
will be passed an error if one occured, otherwise `null`.