Почему DbTestCase not found?

<?php
namespace tests\unit;
use PHPUnit\Framework\TestResult;
use yii\codeception\DbTestCase;
class SynchronizationTest extends DbTestCase
{
    public function testSynchronization()
    {
        $this->assertTrue(true);
    }
    public function testSaveAreas()
    {
        $this->assertTrue(true);
    }
    public function testSaveProjects()
    {
        $this->assertTrue(true);
    }
    public function testSaveEvents()
    {
        $this->assertTrue(true);
    }
    /**
     * Count elements of an object
     * @link http://php.net/manual/en/countable.count.php
     * @return int The custom count as an integer.
     * </p>
     * <p>
     * The return value is cast to an integer.
     * @since 5.1.0
     */
    public function count()
    {
        // TODO: Implement count() method.
    }
    /**
     * Runs a test and collects its result in a TestResult instance.
     *
     * @param TestResult $result
     *
     * @return TestResult
     */
    public function run(TestResult $result = null)
    {
        // TODO: Implement run() method.
    }
}