ServiceProviderWebTest.php

<?php

namespace Drupal\Tests\system\Functional\ServiceProvider;

use Drupal\Tests\BrowserTestBase;

/**
 * Tests service provider registration to the DIC.
 *
 * @group ServiceProvider
 */
class ServiceProviderWebTest extends BrowserTestBase {
    
    /**
     * Modules to enable.
     *
     * @var array
     */
    protected static $modules = [
        'file',
        'service_provider_test',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    
    /**
     * Tests that module service providers get registered to the DIC.
     *
     * Also tests that services provided by module service providers get
     * registered to the DIC.
     */
    public function testServiceProviderRegistrationIntegration() {
        $this->assertTrue(\Drupal::hasService('service_provider_test_class'), 'The service_provider_test_class service has been registered to the DIC');
        // The event subscriber method in the test class calls
        // \Drupal\Core\Messenger\MessengerInterface::addStatus() with a message
        // saying it has fired. This will fire on every page request so it should
        // show up on the front page.
        $this->drupalGet('');
        $this->assertSession()
            ->pageTextContains('The service_provider_test event subscriber fired!');
    }

}