block_theme_suggestions_block example

    $variables = [];
    /** @var \Drupal\Core\Block\BlockPluginInterface $plugin */
    $plugin = $block->getPlugin();
    $variables['elements']['#configuration'] = $plugin->getConfiguration();
    $variables['elements']['#plugin_id'] = $plugin->getPluginId();
    $variables['elements']['#id'] = $block->id();
    $variables['elements']['#base_plugin_id'] = $plugin->getBaseId();
    $variables['elements']['#derivative_plugin_id'] = $plugin->getDerivativeId();
    $variables['elements']['content'] = [];
    $suggestions = block_theme_suggestions_block($variables);
    $this->assertSame([
      'block__system',
      'block__system_menu_block',
      'block__system_menu_block__admin',
      'block__machinename',
    ], $suggestions);
  }

}