If testOnBorrow is set true, testOnConnect is false, and validationQuery is an illegal query, the current implementation will hide the fact that validationQuery never succeeds.

The offending code is in org.apache.tomcat.jdbc.pool.ConnectionPool line 797.

790            //if we reached here, that means the connection
791	            //is either has another principal, is discarded or validation failed.
792	            //we will make one more attempt
793	            //in order to guarantee that the thread that just acquired
794	            //the connection shouldn't have to poll again.
795	            try {
796	                con.reconnect();
797	                if (con.validate(PooledConnection.VALIDATE_INIT)) {

Instead, con.validate(PooledConnection.VALIDATE_BORROW) should be called.