@Nullable
  private IAnnotationDrivenExtension getAnnotationDrivenExtension(Annotation annotation) {
    ExtensionAnnotation extAnn = annotation.annotationType().getAnnotation(ExtensionAnnotation.class);
    if (extAnn == null) return null;
    return getOrCreateExtension(extAnn.value());
  }
Runs global and local extensions for a spec.
spock-core/src/main/java/org/spockframework/runtime/ExtensionRunner.java