public function testDownload($account){
$this->browse(function (Browser $browser) {
$download_path = storage_path('your/download/path');
$url = $browser->driver->getCommandExecutor()->getAddressOfRemoteServer();
$uri = '/session/' . $browser->driver->getSessionID() . '/chromium/send_command';
$body = [
'cmd' => 'Page.setDownloadBehavior',
'params' => ['behavior' => 'allow', 'downloadPath' => $download_path]
];
(new \GuzzleHttp\Client())->post($url . $uri, ['body' => json_encode($body)]);
// Start your test
$browser->visit("http://example.com/export")
//your asserts here
}