There is no guidance I could find on how to allow/disallow blocking in a constructor or static initializer. There is one test that shows how to do it for a static initializer but it would be nicer if it was easier to find. One option could be a dedicated method, e.g. allowBlockingCallsInsideConstructor(String classname), or otherwise provide guidance in the Javadoc on allowBlockingCallsInside and a mention on the Customizations page.