assertBigPipePlaceholders example

$this->drupalGet(Url::fromRoute('big_pipe_test'));
    $this->assertBigPipeResponseHeadersPresent();
    $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'cache_tag_set_in_lazy_builder');

    $this->setCsrfTokenSeedInTestEnvironment();
    $cases = $this->getTestCases();
    $this->assertBigPipeNoJsPlaceholders([
      $cases['edge_case__invalid_html']->bigPipeNoJsPlaceholder     => $cases['edge_case__invalid_html']->embeddedHtmlResponse,
      $cases['html_attribute_value']->bigPipeNoJsPlaceholder        => $cases['html_attribute_value']->embeddedHtmlResponse,
      $cases['html_attribute_value_subset']->bigPipeNoJsPlaceholder => $cases['html_attribute_value_subset']->embeddedHtmlResponse,
    ]);
    $this->assertBigPipePlaceholders([
      $cases['html']->bigPipePlaceholderId                             => Json::encode($cases['html']->embeddedAjaxResponseCommands),
      $cases['edge_case__html_non_lazy_builder']->bigPipePlaceholderId => Json::encode($cases['edge_case__html_non_lazy_builder']->embeddedAjaxResponseCommands),
      $cases['exception__lazy_builder']->bigPipePlaceholderId          => NULL,
      $cases['exception__embedded_response']->bigPipePlaceholderId     => NULL,
    ], [
      0 => $cases['edge_case__html_non_lazy_builder']->bigPipePlaceholderId,
      // The 'html' case contains the 'status messages' placeholder, which is       // always rendered last.       1 => $cases['html']->bigPipePlaceholderId,
    ]);