Spock Spy/Mock not registering the invocations

I have a method in my test class that just calls two other methods. I am trying to write a test that checks that those two methods are actually invoced, but no invocations are registered. Java code I'm testing:

    public void populateEdgeInfo(Map<Actor, SchedulableNode> knownNodes) {
        populateDestinationInfo(knownNodes);
        populateSourceInfo(knownNodes);
    }

My test code:

def "Populating edge info means both source and destination information will be populated" () {
    given:
    actor.getDstChannels() >> []
    actor.getSrcChannels() >> []
    SchedulableNode schedulable = Spy(SchedulableNode, constructorArgs: [actor])

    when:
    schedulable.populateEdgeInfo([:])

    then:
    1 * schedulable.populateDestinationInfo(_)
    1 * schedulable.populateSourceInfo(_)
}

The only thing registered is the call to populateEdgeInfo. Is there something obvious that I am doing wrong? Also tried using Mock instead of Spy to no avail.