CannotAcquireResourceException in Junit

Hi,

I am getting the following error while running bunch of Junit test
cases through “ant test” command----

Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A
ResourcePool could not acquire a resource from its primary factory or
source.

PFA full stack trace.

After execution of 300 test cases I got this error. The setup() method code
snippet is ---

@Before

public void setUp() throws Exception {

entityManager =
entityManagerFactory.createEntityManager();//javax.persistence.EntityManager

entityManager.getTransaction().begin();

}

this method ran for all 300 test cases but didn’t get error .

Another 900 test cases are remaining. I tried running single test cases
from those test cases, getting same error for all.

What is root cause of this error.

Thanks and Regards,

Abhra