Symfony 4.如何使用另一个文件夹进行单元测试？

I have in the folder [project-folder]/assets some docx-documents. For unit tests, I want to use another docx-documents from the folder [project-folder]/tests/resources. Is it possible? How can I say, that $this->rootDir returns [project-folder]/tests/resources? Or are there another ideas to resolve my issue?

public function __construct(EngineInterface $templating, KernelInterface $kernel)
{
    $this->templating = $templating;
    $this->rootDir = $kernel->getProjectDir();
}

public function generateDocxDocument($twigTemplate, $data = [], $docxTemplate = self::DEFAULT_DOCX_TEMPLATE)
{
    $tempFileName = sys_get_temp_dir(). '/' . uniqid();
    $tempDocxFileName = $tempFileName . '.docx';

    $filename = $this->rootDir . '/assets/' . $docxTemplate;
}