How to test DAO layer in Java Web application using Mockito and PowerMock in Eclipse and Tomcat 8?

I'm new to JavaEE and now i have troubles with testing my app using Mockito and PowerMock. I found how to test servlets but my DAO layer is configurated with Tomcat Connection Pool with MySQL and I can't find how to make it work. Almost all of my classes use DB to get information and i can`t test them nice because of this problem. Help me, please.