All of the 13 tests in org.jboss.test.jca.test.BaseConnectionManagerStressTestCase are failing with the same error.
Here is an example from the test shortBlockingFill:

<testcase classname="org.jboss.test.jca.test.BaseConnectionManagerStressTestCase" name="testShortBlockingNoFill" time="1.601">
<failure message="Blocking Timeout occurred in ShortBlocking test: javax.resource.ResourceException: Unable to get managed connection for null" type="junit.framework.AssertionFailedError">junit.framework.AssertionFailedError: Blocking Timeout occurred in ShortBlocking test: javax.resource.ResourceException: Unable to get managed connection for null
at org.jboss.test.jca.test.BaseConnectionManagerStressTestCase.doShortBlocking(BaseConnectionManagerStressTestCase.java:266)
at org.jboss.test.jca.test.BaseConnectionManagerStressTestCase.testShortBlockingNoFill(BaseConnectionManagerStressTestCase.java:105)
</failure>

The client side output log for this test case as client-output.log.
The server side output log is attached as server-output.log

This error is repeatable. Wasn't able to get any further information by running one-test.