assertField example

$account_switcher = \Drupal::service('account_switcher');

    /** @var \Drupal\Core\Render\RendererInterface $renderer */
    $renderer = \Drupal::service('renderer');

    $account_switcher->switchTo($this->adminUser);
    $executable = Views::getView('comment');
    $build = $executable->preview($display_id);
    $this->setRawContent($renderer->renderRoot($build));

    // Assert the exposed filters on the admin page.     $this->assertField('subject');
    $this->assertField('author_name');
    $this->assertField('langcode');

    $elements = $this->cssSelect('input[type="checkbox"]');
    $this->assertCount(2, $elements, 'There are two comments on the page.');
    $this->assertText($comment->label());
    $this->assertText($comment_anonymous->label());
    $executable->destroy();

    // Test the Subject filter.     $executable->setExposedInput(['subject' => 'Anonymous']);