Test Config Backend Model

test_config_backend_model.php

<?php

use Magento\Framework\App\Area;
use Magento\Framework\App\Config\ScopeConfigInterface;

require __DIR__ . '/app/bootstrap.php';

class TestConfigBackendModelApp extends \Magento\Framework\App\Http implements \Magento\Framework\AppInterface
{
    /**
     * @var ScopeConfigInterface
     */
    private $scopeConfig;

    public function launch()
    {
        $this->_state->setAreaCode(Area::AREA_FRONTEND);
        $this->_objectManager->configure($this->_configLoader->load(Area::AREA_FRONTEND));

        $this->scopeConfig = $this->_objectManager->get(ScopeConfigInterface::class);

        $body[] = print_r($this->scopeConfig->getValue('newrelicreporting/general/insights_insert_key'), true);

        $this->_response->setBody(implode(PHP_EOL, $body) . PHP_EOL);
        //the method must end with this line
        return $this->_response;
    }

    public function catchException(\Magento\Framework\App\Bootstrap $bootstrap, \Exception $exception)
    {
        return false;
    }
}

$bootstrap = \Magento\Framework\App\Bootstrap::create(BP, $_SERVER);

/** @var \Magento\Framework\App\Http $app */
$app = $bootstrap->createApplication('TestConfigBackendModelApp');
$bootstrap->run($app);