What exactly does test-connection-in-pool do?

Issue

• Can you tell me the exact mechanism of the "Test Connection" (test-connection-in-pool) function for a JBoss EAP 6.2.0 data source?

• The users are trying to troubleshoot connection problems, and they need to know if it just executes a ping method in the JDBC driver and back to JBoss, or makes an actual connection to the database schema, etc.