yii2 关于自定义errorHandler的疑问

//配置文件web.php加了下面一个配置
'errorHandler' => [
    'errorAction' => 'test/error',
],

//TestController.php文件的内容

namespace app\controllers;
use Yii;
use yii\web\Controller;
use yii\web\HttpException;

class TestController extends Controller
{
    public function actionIndex()
    {
        throw new HttpException(409, 'adf');
    }
    public function actionError()
    {
        echo 'a';die;
    }
}

'response' => [
    'format' => yii\web\Response::FORMAT_JSON,
    'charset' => 'UTF-8',
],

//配置文件web.php加了下面一个配置
'errorHandler' => [
    'errorAction' => 'test/error',
],

//TestController.php文件的内容

namespace app\controllers;
use Yii;
use yii\web\Controller;
use yii\web\HttpException;

class TestController extends Controller
{
    public function actionIndex()
    {
        throw new HttpException(409, 'adf');
    }
    public function actionError()
    {
        echo 'a';die;
    }
}

'response' => [
    'format' => yii\web\Response::FORMAT_JSON,
    'charset' => 'UTF-8',
],