@Test(expected = IllegalArgumentException.class)
  public void voidProducerThrowsException() throws Exception {
    class VoidProducer {
      @Produce public void things() {}
    }
    bus.register(new VoidProducer());
  }
Tests that events are distributed to any subscribers to their type or any
supertype, including interfaces and superclasses.

Also checks delivery ordering in such cases.
otto/src/test/java/com/squareup/otto/BusTest.java