Namespaces not working with Codeception (Yii2) - namespaces

Question

Im using Codeception in Yii2 to make acceptance tests and there's no way to access my models because namespaces are not working into these tests.
I have this in my tests/_bootstrap.php
require(__DIR__ . '/../vendor/autoload.php');
require(__DIR__ . '/../vendor/yiisoft/yii2/Yii.php');
$config = require(__DIR__ . '/../console/config/main.php');
//
$application = new yii\console\Application( $config );
## Added (#vitalik_74)
Yii::setAlias('#tests', dirname(__DIR__));
This in my console/config/main
<?php
$params = array_merge(
require(__DIR__ . '/params.php'),
require(__DIR__ . '/params-local.php')
);
return [
'id' => 'app-console',
'basePath' => dirname(__DIR__),
'bootstrap' => ['log'],
'controllerNamespace' => 'console\controllers',
'components' => [
'log' => [
'targets' => [
[
'class' => 'yii\log\FileTarget',
'levels' => ['error', 'warning'],
],
],
],
],
'params' => $params,
];
<?php
return [
'adminEmail' => 'admin#example.com',
'supportEmail' => 'support#example.com',
'user.passwordResetTokenExpire' => 3600,
];
And this is one of the wannabe-tests:
<?php namespace tests\acceptance;
use \AcceptanceTester;
use backend\models\User; ## I have tried writing it with a / at the beggining
class ListUserCest
{
public function _before(AcceptanceTester $I)
{
}
public function _after(AcceptanceTester $I)
{
}
public function init(AcceptanceTester $I)
{
$this->login($I);
if( User::find()->exists() )
$I->amGoingTo('List Users having at least one');
else
$I->amGoingTo('List Users having any');
}
...
I get this error when running the tests:
PHP Fatal error: Class 'backend\models\User' not found in /var/www/project/tests/acceptance/ListUserCest.php on line 21
Error: Class 'backend\models\User' not found
Please, help me, I have tried everything I know
EDIT
Now (after adding the line recommended by vitalik_74) I can use for example, \Yii methods into the tests but witout the web application configuration, just the console configuration.
I mean, I still can't use \backend\models\User and I can't neither access the Yii::$app->user status (to check if user is logged, for example).
The User model is just a common ActiveRecord model with his tableName, rules, attributeLabels, and some relational methods like getProfile().
It works out of the tests
<?php
namespace backend\models;
use common\helpers\MathHelper;
use backend\models\AntropometricData;
use Yii;
class User extends \yii\db\ActiveRecord
{
/**
* #inheritdoc
*/
public static function tableName()
{
return 'user';
}
...

Answer 1

Put the next code to tests/_bootstrap.php:
require('vendor/autoload.php');
require('vendor/yiisoft/yii2/Yii.php');
$config = require('config/web.php');
(new yii\web\Application($config));