The SimpleDispatchPolicyTest and RoundRobinDispatchPolicyTest were failing on my single proc powerbook. The parent of the MessageIdList was being called before the clild had processed the message which cause the test to not wait till the childeren had processed the messages so tests would fail due to short counts.
incubator/activemq/trunk/activemq-core/src/test/java/org/apache/activemq/util/MessageIdList.java