Why is there a problem when testing unit tests if there are several methods?

Question

Yii

Hello!
The project is being unit tested on yii2 using codeception.
Command in progress:
php codecept.phar run --debug unit ExampleTest
Test code:

<?php

class ExampleTest extends \Codeception\Test\Unit
{
    /**
     * @var \UnitTester
     */
    protected $tester;

    protected function _before()
    {
    }

    protected function _after()
    {
    }

    // tests
    public function testSomeFeature()
    {

    }

    public function testSomeFeature2()
    {

    }
}

As a result of the test, on the testSomeFeature2() method, an error occurs:

- ExampleTest: Some feature
  [Database] Transaction started
+ ExampleTest: Some feature (0.01s)
  [Database] Transaction cancelled; all changes reverted.
- ExampleTest: Some feature2
Fatal error: Cannot declare class Yii, because the name is already in use in C:\OSPanel\domains\yii2tests.loc\vendor\yiisoft\yii2\Yii.php on line 21

If, to test only 1 method, then everything works fine.
config files.
unit.suite.xml

# Codeception Test Suite Configuration

# suite for unit (internal) tests.
# RUN `build` COMMAND AFTER ADDING/REMOVING MODULES.

class_name: UnitTester
modules:
    enabled:
      - Asserts
      - Yii2:
            configFile: 'tests/config/unit.php'
            part: [orm, email]

/tests/config/unit.php

<?php
/**
 * Application configuration for acceptance tests
 */
require(__DIR__ . '/../../vendor/autoload.php');
require(__DIR__ . '/../../vendor/yiisoft/yii2/Yii.php');

return yii\helpers\ArrayHelper::merge(
    require(__DIR__ . '/../../config/web.php'),
    require(__DIR__ . '/config.php'),
    []
);

Why does the error "Fatal error: Cannot declare class Yii, because the name is already in use" appear when testing several methods and how to fix it?