@Override
  public void prune() {}
Prevent this node from being pruned. The default logic would prune it, as it
<ul>
  <li>is no test,</li>
  <li>has no test descendents and</li>
  <li>may not register new tests during execution</li>
</ul>

Without this empty override, the node is thrown away and the error is not reported.
spock-core/src/main/java/org/spockframework/runtime/ErrorSpecNode.java