protected function createBrowsersFor(Closure $callback)
    {
        if (count(static::$browsers) === 0) {
            static::$browsers = collect([$this->newBrowser($this->createWebDriver())]);
        }

        $additional = $this->browsersNeededFor($callback) - 1;

        for ($i = 0; $i < $additional; $i++) {
            static::$browsers->push($this->newBrowser($this->createWebDriver()));
        }

        return static::$browsers;
    }