After upgrading to JNA 5.2.0, running FBConnectionTest.testLockTable on EMBEDDED hangs the Java process on exit. This suggests that the connection was not properly closed or some other resource was kept around. The problem only seems to be reproducible on Java 7 and 8, or on Java 11 when compiled on Java 8.
As a temporary workaround a call to fb_shutdown was added to this test class in an @AfterClass method, but that is hardly a proper solution. This needs to be investigated further if things are not properly closed or released, or otherwise a more robust cleanup is necessary. See also some of the comments on https://github.com/FirebirdSQL/jaybird/pull/21
This is also possibly related to