using different datasource during junit tests

[Matthew Broadhead]

i am trying to test some business logic that depends heavily on the 
results of calls to entitymanager.  i would like to keep the 
persistence.xml exactly as it is in the main project but basically load 
in a different database underneath.  is there a way to initialise the 
entitymanager and point it to a development database for the duration of 
the tests?