TestAttributesBlock.php

<?php

namespace Drupal\layout_builder_test\Plugin\Block;

use Drupal\Core\Block\BlockBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Provides a 'TestAttributes' block.
 *
 * @Block(
 *   id = "layout_builder_test_test_attributes",
 *   admin_label = @Translation("Test Attributes"),
 *   category = @Translation("Test")
 * )
 */
class TestAttributesBlock extends BlockBase {
  
  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function build() {
    $build = [
      '#attributes' => [
        'class' => [
          'attribute-test-class',
        ],
        'custom-attribute' => 'test',
      ],
      '#markup' => $this->t('Example block providing its own attributes.'),
      '#contextual_links' => [
        'layout_builder_test' => [
          'route_parameters' => [],
        ],
      ],
    ];
    return $build;
  }

}