YII2 Codeception - create fixture. [Error] Class 'tests\fixtures\UserFixture' not found

Question

I'm using YII2 2.0.10, basic. It seems that it don't use yii-codeception module anymore. So documentation from this page is not actual: http://www.yiiframework.com/doc-2.0/guide-test-fixtures.html

My problem is that I can't load fixture to my test. I'm using such way:

tests\unit\models\UserTest.php

<?php
namespace tests\models;
use app\models\User;
use tests\fixtures\UserFixture;

class UserTest extends \Codeception\Test\Unit
{
    public function testFindUserById()
    {
        // load fixtures
        $this->tester->haveFixtures([
            'user' => [
                'class' => UserFixture::className(),
                // fixture data located in tests/_data/user.php
                'dataFile' => codecept_data_dir() . 'user.php'
            ]
        ]);
        // get first user from fixtures
        $this->tester->grabFixture('user', 0);
        ...

tests\fixtures\UserFixture.php

namespace tests\fixtures;

use yii\test\ActiveFixture;

class UserFixture extends ActiveFixture
{
    public $modelClass = 'dektrium\user\models\User';
}

And have some data returned from tests\fixtures\data\user.php

After vendor/codeception/base/codecept run I get

2) UserTest: Find user by id
 Test  tests/unit/models/UserTest.php:testFindUserById

  [Error] Class 'tests\_fixtures\UserFixture' not found

#1  tests\models\UserTest->testFindUserById

What I'm doing wrong?