yii2-app-basic/tests/codeception/config/functional.php

<?php
$_SERVER['SCRIPT_FILENAME'] = YII_TEST_ENTRY_FILE;
$_SERVER['SCRIPT_NAME'] = YII_TEST_ENTRY_URL;

/**
 * Application configuration for functional tests
 */
return yii\helpers\ArrayHelper::merge(
    require(__DIR__ . '/../../../config/web.php'),
    require(__DIR__ . '/config.php'),
    [
        'components' => [
            'db' => [
                'dsn' => 'mysql:host=localhost;dbname=yii2_basic_functional',
            ],
        ],
    ]
);