How to deal with DTT with a specific paragraph like "Quote" and the correct parent classes following best practices.

EntityBundleTestBase.php

<?php

  declare(strict_types=1);

  namespace Drupal\Tests\server_general\ExistingSite;

  use Drupal\Tests\drupal_test_assertions\Assertions\EntityTrait;
  use Drupal\Tests\drupal_test_assertions\Assertions\FieldsTrait;
  use weitzman\DrupalTestTraits\ExistingSiteBase;

  /**
   * Abstract base class for testing entity bundles.
   *
   * Automatically runs field existence and required/optional assertions
   * for every concrete test class via testFields().
   */
  abstract class EntityBundleTestBase extends ExistingSiteBase implements RequiredAndOptionalFieldTestInterface {

    use EntityTrait;
    use FieldsTrait;

    /**
     * Tests required and optional fields for this entity bundle.
     */
    public function testFields(): void {
      $entity_type = $this->getEntityType();
      $entity_bundle = $this->getEntityBundle();

      $this->assertEntityExists($entity_type, $entity_bundle);

      foreach ($this->getRequiredFields() as $field_name) {
        $this->assertFieldIsRequired($field_name, $entity_type, $entity_bundle);
      }

      foreach ($this->getOptionalFields() as $field_name) {
        $this->assertFieldIsNotRequired($field_name, $entity_type, $entity_bundle);
      }
    }

  }

FileCreationTrait.php

<?php

declare(strict_types=1);

namespace Drupal\Tests\server_general\Traits;

use Drupal\Core\File\FileExists;
use Drupal\file\FileInterface;
use weitzman\DrupalTestTraits\DrupalTrait;

/**
 * Provides file entity creation for tests using committed test assets.
 *
 * Assets live in tests/assets/ and are copied to public:// with
 * FileExists::Replace, so files never accumulate across test runs. The
 * physical file persists in public:// intentionally — this is safe for
 * parallel tests and avoids teardown race conditions.
 *
 * Available assets:
 * - test-image.png
 * - test-image.jpg
 * - test-file.pdf
 */
trait FileCreationTrait {

  use DrupalTrait;

  const ASSETS_PATH = 'modules/custom/server_general/tests/assets/';

  /**
   * Creates a File entity from a committed test asset.
   *
   * @param string $filename
   *   The asset filename (e.g. 'test-image.png'). Must exist in tests/assets/.
   *
   * @return \Drupal\file\FileInterface
   *   The saved File entity, marked for automatic cleanup.
   */
  protected function createFileEntity(string $filename): FileInterface {
    $source = \Drupal::root() . '/' . self::ASSETS_PATH . $filename;
    $uri = \Drupal::service('file_system')
      ->copy($source, 'public://' . $filename, FileExists::Replace);

    /** @var \Drupal\file\FileInterface $file */
    $file = \Drupal::entityTypeManager()
      ->getStorage('file')
      ->create([
        'uri' => $uri,
        'status' => 1,
      ]);
    $file->setPermanent();
    $file->save();
    $this->markEntityForCleanup($file);

    return $file;
  }

}

ParagraphCreationTrait.php

 <?php

  declare(strict_types=1);

  namespace Drupal\Tests\server_general\Traits;

  use Drupal\paragraphs\Entity\Paragraph;
  use Drupal\paragraphs\ParagraphInterface;
  use weitzman\DrupalTestTraits\DrupalTrait;

  /**
   * Helps in creation of Paragraph entities in tests.
   */
  trait ParagraphCreationTrait {

    use DrupalTrait;

    /**
     * Creates a Paragraph and marks it for automatic cleanup.
     *
     * @param array $settings
     *   The settings to pass to Paragraph creation.
     *
     * @return \Drupal\paragraphs\ParagraphInterface
     *   The created Paragraph entity.
     */
    protected function createParagraph(array $settings = []): ParagraphInterface {
      /** @var \Drupal\paragraphs\ParagraphInterface $entity */
      $entity = Paragraph::create($settings);
      $entity->save();
      $this->markEntityForCleanup($entity);

      return $entity;
    }

    /**
     * Extract the reference values for a paragraph.
     *
     * @param \Drupal\paragraphs\ParagraphInterface $paragraph
     *   The paragraph.
     *
     * @return array
     *   Reference values containing target_id and target_revision_id.
     */
    protected function getParagraphReferenceValues(ParagraphInterface $paragraph): array {
      return [
        'target_id' => $paragraph->id(),
        'target_revision_id' => $paragraph->getRevisionId(),
      ];
    }

  }

QuoteParagraphTest.php

 <?php

  declare(strict_types=1);

  namespace Drupal\Tests\server_general\ExistingSite;

  use Drupal\Tests\server_general\Traits\FileCreationTrait;
  use Drupal\Tests\server_general\Traits\ParagraphCreationTrait;
  use Symfony\Component\HttpFoundation\Response;
  use weitzman\DrupalTestTraits\Entity\MediaCreationTrait;

  /**
   * Test 'Quote' paragraph type.
   */
final class QuoteParagraphTest extends EntityBundleTestBase {

    use FileCreationTrait;
    use MediaCreationTrait;
    use ParagraphCreationTrait;

    /**
     * {@inheritdoc}
     */
    public function getEntityType(): string {
      return 'paragraph';
    }

    /**
     * {@inheritdoc}
     */
    public function getEntityBundle(): string {
      return 'quote';
    }

    /**
     * {@inheritdoc}
     */
    public function getRequiredFields(): array {
      return [
        'field_body',
        'field_image',
      ];
    }

    /**
     * {@inheritdoc}
     */
    public function getOptionalFields(): array {
      return [
        'field_subtitle',
      ];
    }

    /**
     * Test render of the paragraph.
     */
    public function testRender(): void {
      $file = $this->createFileEntity('test-image.png');
      $media = $this->createMedia([
        'bundle' => 'image',
        'name' => 'Test image',
        'field_media_image' => [
          'target_id' => $file->id(),
          'alt' => 'Test image alt',
        ],
      ]);

      $body = 'This is the body';
      $subtitle = 'This is the subtitle';

      $paragraph = $this->createParagraph([
        'type' => $this->getEntityBundle(),
        'field_body' => $body,
        'field_subtitle' => $subtitle,
        'field_image' => [
          'target_id' => $media->id(),
        ],
      ]);

      $node = $this->createNode([
        'title' => 'Landing Page',
        'type' => 'landing_page',
        'field_paragraphs' => [
          $this->getParagraphReferenceValues($paragraph),
        ],
        'moderation_state' => 'published',
      ]);
      $node->setPublished()->save();

      $this->drupalGet($node->toUrl());
      $this->assertSession()->statusCodeEquals(Response::HTTP_OK);
      $this->assertSession()->elementTextContains('css', '.paragraph--type--quote', $body);
      $this->assertSession()->elementTextContains('css', '.paragraph--type--quote', $subtitle);
    }

  }

RequiredAndOptionalFieldTestInterface.php

<?php

  declare(strict_types=1);

  namespace Drupal\Tests\server_general\ExistingSite;

  /**
   * Interface defining the contract for entity bundle field tests.
   */
  interface RequiredAndOptionalFieldTestInterface {

    /**
     * Returns the entity type to test.
     *
     * @return string
     *   An entity type name (e.g. 'node', 'paragraph').
     */
    public function getEntityType(): string;

    /**
     * Returns the entity bundle to test.
     *
     * @return string
     *   A bundle name (e.g. 'quote', 'landing_page').
     */
    public function getEntityBundle(): string;

    /**
     * Returns the required fields for this entity bundle.
     *
     * @return string[]
     *   Array of required field names.
     */
    public function getRequiredFields(): array;

    /**
     * Returns the optional fields for this entity bundle.
     *
     * @return string[]
     *   Array of optional field names.
     */
    public function getOptionalFields(): array;

  }