What is Back End Testing and Its Importance

What is back end testing?

Back-end testing is testing a system that runs behind the front-end (GUI Applications). It can be Database testing, Server Side testing.

Talking about Database testing, it can involve:

-> Data validity testing

-> Data integrity testing

-> Performance related to Database specially when working with Views and Indexes.

-> Testing of procedures, functions and triggers.

Server Side testing can involve the servers running on Unix (Solaris, AIX)/Linux, mainframes systems. The parameter to be monitored can be:

-> Server logs

-> Jvm logs (If it’s a Java based application)

-> Checking the Garbage Collector (GC) values and see if it’s happening properly or not by tuning its parameters properly.

-> Server downtime

-> Sever response time

-> Checking batch processes in UNIX

Why is Back end testing required?

Assume that you're thinking client-server or web. If you test the application on the front end only you can see if the data was stored and retrievd correctly. You can't see if the servers are in an error state or not. Many server processes are monitored by another process. If they crash, they are restarted. You can't see that without looking at it. 
The data may not be stored correctly either but the front end may have cached data lying around and it will use that instead. The least you should be doing is verifying the data as stored in the database. 
It is easier to test data being transferred on the boundaries and see the results of those transactions when you can set the data in a driver.