"Perform tests" problem using app engine datastore.

Add a project, setup the database using the "persistence setup --provider DATANUCLEUS --database GOOGLE_APP_ENGINE" command, an entity, a field and a controller.
The "perform tests" command produces this error, which is also reported by other forum members(please check the forum post):

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T E S T S
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Running org.firstats.web.domain.CategoryIntegrationTest
2010-11-07 18:10:55,583 [main] ERROR DataNucleus.Transaction - Opera
tion rollback failed on resource: org.datanucleus.store.appengine.DatastoreXARes
[email protected], error code UNKNOWN and transaction: [DataNucleus Transaction, ID=Xid= enlisted resources=[[email protected]]]
2010-11-07 18:14:58,383 [main] ERROR DataNucleus.Transaction - Opera
tion rollback failed on resource: org.datanucleus.store.appengine.DatastoreXARes
[email protected], error code UNKNOWN and transaction: [DataNucleus Transaction, ID=Xid= enlisted resources=[[email protected]]]
Tests run: 9, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 6.5
8 sec <<< FAILURE!

Results :

Tests in error:
testCountCategorys(org.firstats.web.domain.CategoryIntegrationTes
)

Tests run: 9, Failures: 0, Errors: 1, Skipped: 0

[INFO] ------------------------------------------------------------
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[ERROR] BUILD FAILURE
[INFO] ------------------------------------------------------------
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[INFO] There are test failures.