assertWidthClassApplied example

'class' => 'layout--threecol-section--',
      ],
    ];
    foreach ($width_options as $width_option) {
      $width = $width_option['default_width'];
      $assert_session->linkExists('Add section');
      $page->clickLink('Add section');
      $this->assertNotEmpty($assert_session->waitForElementVisible('css', "#drupal-off-canvas a:contains(\"{$width_option['label']}\")"));
      $page->clickLink($width_option['label']);
      $this->assertNotEmpty($assert_session->waitForElementVisible('css', '#drupal-off-canvas input[type="submit"][value="Add section"]'));
      $page->pressButton("Add section");
      $this->assertWidthClassApplied($width_option['class'] . $width);
      foreach ($width_option['additional_widths'] as $width) {
        $width_class = $width_option['class'] . $width;
        $assert_session->linkExists('Configure Section 1');
        $page->clickLink('Configure Section 1');
        $this->assertNotEmpty($assert_session->waitForElementVisible('css', '#drupal-off-canvas input[type="submit"][value="Update"]'));
        $page->findField('layout_settings[column_widths]')->setValue($width);
        $page->pressButton("Update");
        $this->assertWidthClassApplied($width_class);
      }
      $assert_session->linkExists('Remove Section 1');
      $this->clickLink('Remove Section 1');