Unit test cases in pimcore, getting error while executing test cases

Question

pimcore v 6.6

im trying to unit test by codeception, i have installed codception and tests/ folder created under my project directory. But when im calling the service function getting below error

Error attached

**[PHPUnit\Framework\Exception] Use of undefined constant PIMCORE_PROJECT_ROOT - assumed ‘PIMCORE_PROJECT_ROOT’ (this will throw an Error in a future version of PHP)

src/GenericBundle/Service/PdfImportService.php:31**

File name for test is PdfImportServiceTest.php

public function testGetFilesArray() { 
    $pdfService = new PdfImportService(); 
    $this->assertFalse($pdfService->getFilesArray()); 
}

I have added bootstrap.php file inside tests/ path

code is here

// tests/bootstrap.php

include “./vendor/autoload.php”;

\Pimcore\Bootstrap::setProjectRoot(); 
\Pimcore\Bootstrap::bootstrap();

===================================================

added another file named codeception.dist.yml

namespace: Tests support_namespace: 
           Support actor_suffix: Tester 
paths: 
    tests: . 
    output: ./_output 
    data: ./Support/Data 
    support: ./Support 
    envs: ./_envs 
settings: 
    bootstrap: _bootstrap.php 
    colors: true 
params: - env 
extensions: 
    enabled: - Codeception\Extension\RunFailed

============================================================= also i have added _bootstrap.php && codeception.yml file inside tests/ as per in the pimcore doc

when im executing this test case, its calling constructor of actual service file and there we have defined constant path for the file, but this test case is not working. Actual function from the backend is working

in some services im getting get container null error… Please check the link for error.

I followed pimcore unit testing document + symfony documnet + codception document. But it didnt work for me. Im stuck with this from 3 days.

Please let me know how to resolve it.

Thanks in advance