Is testing through secondary testing app white box testing?

Why do we need White Box Testing ?

• If in an organization Black box and other testing team tests a software and gives the nod (after all kinds of testing & validation) for release then why do we need another testing team in the form of white box testers to test it ? Aren't we wasting time & resource ? At times we need to see how the logic is implemented and due to this we need W-Box testing. But is it the only reason ? Please provide me the critical reasons for having white box testing team in a organization. Thanks in advance.

• Answer:

  In white box testing we not only check the way things are working but also it supplements the black box testing as we can not make exhaustive test cases due to our limited resources and the cost-benefit trade-off. There are funtions/methods that would give you correct output after giving it inputs but there may be an input test case which you did not think about and this may create problem at the client side. So if you get a correct output for certian inputs, this doesn't mean that you have completly checked your function/method. For this we need white box testing to completly understand the mechanism and the way it is producing the output using certian input. White box testing or the team of testers is not a wastage of resources as they help you find out the problems or bugs in the software which if discovered by the customers will resutl in lost business and bad name for the company.