我是c3op的新手，对使用感到困惑：

c3p0.idle_test_period

在此链接中：如何配置C3P0连接池

idleTestPeriod :  Must be set in hibernate.cfg.xml (or hibernate.properties), Hibernate default:  
0, If this is a number greater than 0, c3p0 will test all idle, pooled but unchecked-out  
connections, every this number of seconds.

这种测试（空闲，池连接）的目的是什么，以及c3p0.idle_test_period和c3p0.timeout之间的关系？