public function test_pay()
{
$today = Carbon::today()->toDateString();
$billet = factory(Billet::class)->create(['discharge_date' => null]);
$this->put('api/v1/billet/' . $billet->id . '/pay', ['discharge_date' => $today]);
$this->seeStatusCode(200);
$this->seeInDatabase('billets', ['id' => $billet->id, 'discharge_date' => $today]);
}