If jdbcapi.AuthenticationTest is run without changing the derby.stream.error.extendedDiagSeverityLevel as is done in the test, it generates thread dumps and javacores for IBM jvms. I beleive the errors in this test are expected user errors and not crashes so they should not generate a thread dump or javacore. To reproduce remove this line from test:
//Derby-4856,set the property to avoid thread dump and diagnostic info
Until fixed, users can work around the issue by setting derby.stream.error.extendedDiagSeverityLevel to 50000 as is done in the test.