为什么我需要在Spring应用程序上下文中定义Hibernate-JPA供应商适配器？

I spent days and days trying to get a working database connection for my Spring/JPA(Hibernate) integration tests, troubleshooting mysterious "No Database Context Found" errors, and I finally got it working, but I don't understand why I had to do what I did.I spent days and days trying to get a working d