class PlaceholderMessageTest

class PlaceholderMessageTest extends BrowserTestBase {
  
  /**
   * Modules to enable.
   *
   * @var array
   */
  protected static $modules = [
    'render_placeholder_message_test',
  ];
  
  /**
   * {@inheritdoc}
   */
  protected $defaultTheme = 'stark';
  
  /**
   * Tests rendering of message placeholder.
   */
  public function testMessagePlaceholder() {
    $messages_markup = '<div role="contentinfo" aria-label="Status message"';
    $test_routes = [
      // Messages placeholder rendered first.
'render_placeholder_message_test.first',
      // Messages placeholder rendered after one, before another.
'render_placeholder_message_test.middle',
      // Messages placeholder rendered last.
'render_placeholder_message_test.last',
    ];
    $assert = $this->assertSession();
    foreach ($test_routes as $route) {
      // Verify that we start off with zero messages queued.
      $this->drupalGet(Url::fromRoute('render_placeholder_message_test.queued'));
      $assert->responseNotContains($messages_markup);
      // Verify the test case at this route behaves as expected.
      $this->drupalGet(Url::fromRoute($route));
      $assert->elementContains('css', 'p.logged-message:nth-of-type(1)', 'Message: P1');
      $assert->elementContains('css', 'p.logged-message:nth-of-type(2)', 'Message: P2');
      $assert->responseContains($messages_markup);
      $assert->elementExists('css', 'div[aria-label="Status message"] ul');
      $assert->elementContains('css', 'div[aria-label="Status message"] ul li:nth-of-type(1)', 'P1');
      $assert->elementContains('css', 'div[aria-label="Status message"] ul li:nth-of-type(2)', 'P2');
      // Verify that we end with all messages printed, hence again zero queued.
      $this->drupalGet(Url::fromRoute('render_placeholder_message_test.queued'));
      $assert->responseNotContains($messages_markup);
    }
  }

}