ConcreteSomethingImportServiceTest.php

<?php
declare(strict_types=1);

namespace Vendor\MyExtenstion\Test\Functional\Service;

use …
use TYPO3\TestingFramework\Core\Functional\FunctionalTestCase;

class ConcreteSomethingImportServiceTest extends FunctionalTestCase
{
    /**
     * @var string[]
     */
    protected $testExtensionsToLoad = [
        'typo3conf/ext/my_extension'
    ];

    /**
     * @test
     */
    public function importDoesItRight(): void
    {
        // do something here …
        $this->assertCSVDataSet('EXT:my_extension/Test/Functional/Fixtures/DatabaseAssertions/importSomething.csv');
    }

    protected function setUp(): void
    {
        parent::setUp();
        // Core DataHandler requires a backend user
        $this->setUpBackendUserFromFixture(1);
        $this->importDataSet('EXT:my_extension/Test/Functional/Fixtures/defaultPages.xml');
    }
}