In your situation, I would isolate the calls to Jasper in a small "JasperReportServer" class (it needs to be small to reduce the risk of bugs there), and use Mockito to check the behaviour of the higher-level class that is using it.
Ideally, the JasperReportServer class would be so simple that I wouldn't even unit-test it. However, I do sometimes create a limited number of integration tests to verify that JasperReportServer works OK (although these tests end up being rather brittle, since they rely on the state of an external server that is not controlled well by the tests).