title: Assert attribute value contrains specifict string
body: <p>I'm trying to assert that when selecting a tab from <a href="https://demoqa.com/tabs/" rel="nofollow noreferrer">https://demoqa.com/tabs/</a> the selected tab contains <code>aria-selected="true"</code>.</p>
  
  <pre><code>var attributeValue = tabsPage.SecondTab.GetAttribute("aria-selected");
  Assert.AreEqual(attributeValue, "true");
  </code></pre>
  
  <p>doesn't seem to work.</p>
  
  <p>When debugging <code>attributeValue</code> is <code>null</code></p>