title: Negative Test in SAPUI5 Using OPA
body: <p>Is there a way, to check with OPA-Testing, if an element does <strong>not</strong> exist?</p>
  
  <p>For example the test succeeds, if the waitFor#success callback is not executed and an error message will be shown?</p>
  
  <p>I have an use case, where a button shall be shown or not depending on a very important model property. I want to check this on every deployment with an OPA Test.</p>
  
  <p>The button property is bound to visible, and if the property is false, the button doesnt appear in the DOM and can not be checked for its state because of that.</p>