function whilst(test, iteratee, callback) {
        callback = onlyOnce(callback);
        var _fn = wrapAsync(iteratee);
        var _test = wrapAsync(test);
        var results = [];

        function next(err, ...rest) {
            if (err) return callback(err);
            results = rest;
            if (err === false) return;
            _test(check);
        }

        function check(err, truth) {
            if (err) return callback(err);
            if (err === false) return;
            if (!truth) return callback(null, ...results);
            _fn(next);
        }

        return _test(check);
    }
Repeatedly call `iteratee`, while `test` returns `true`. Calls `callback` when
stopped, or an error occurs.

@name whilst
@static
@memberOf module:ControlFlow
@method
@category Control Flow
@param {AsyncFunction} test - asynchronous truth test to perform before each
execution of `iteratee`. Invoked with (callback).
@param {AsyncFunction} iteratee - An async function which is called each time
`test` passes. Invoked with (callback).
@param {Function} [callback] - A callback which is called after the test
function has failed and repeated execution of `iteratee` has stopped. `callback`
will be passed an error and any arguments passed to the final `iteratee`'s
callback. Invoked with (err, [results]);
@returns {Promise} a promise, if no callback is passed
@example

var count = 0;
async.whilst(
    function test(cb) { cb(null, count < 5); },
    function iter(callback) {
        count++;
        setTimeout(function() {
            callback(null, count);
        }, 1000);
    },
    function (err, n) {
        // 5 seconds have passed, n = 5
    }
);