DrupalBlockCachePerPage.php

<?php

namespace Drupal\test_module\Plugin\Block;

use Drupal\Core\Block\BlockBase;

/**
 * Provides a 'Test block' Block.
 *
 * @Block(
 *   id = "test_block",
 *   admin_label = @Translation("Test block"),
 *   category = @Translation("Test block"),
 * )
 * 
 * Drupal Cache Contexti
 * https://www.drupal.org/docs/8/api/cache-api/cache-contexts
 */
class TestBlock extends BlockBase {

  public function build() {
    $node = \Drupal\node\Entity\Node::load(1);
    $node_title = $node->getTitle();

    return [
      '#markup' => $this->t('The title of node #1 is: ') . $node_title,
      '#cache' => [
        'contexts' => [
          'url.path',
        ],
      ],
    ];
  }

}