@Produce public String produceString() {
        calls++;
        if (calls > 1) {
          fail("Should only have been called once, then unregistered and never called again.");
        }
        return "Please enjoy this hand-crafted String.";
      }
Test case for subscribers which unregister while handling an event.
otto/src/test/java/com/squareup/otto/UnregisteringHandlerTest.java