title: How to test not equal with matcher in flutter
body: <p>I'm doing testing on render objects in Flutter. I'd like to check for inequality like this (simplified):</p>
  
  <pre><code>testWidgets('render object heights not equal', (WidgetTester tester) async {
  
    final renderObjectOneHeight = 10;
    final renderObjectTwoHeight = 11;
  
    expect(renderObjectOneHeight, notEqual(renderObjectTwoHeight));
  });
  </code></pre>
  
  <p>I made up <code>notEqual</code> because it doesn't exist. This doesn't work either:</p>
  
  <ul>
  <li><code>!equals</code></li>
  </ul>
  
  <p><em>I found a solution that works so I am posting my answer below Q&amp;A style. I welcome any better solutions, though.</em></p>