What are the reasons behind to perform white box testing?

There are three main reasons behind performing the white box testing. 

1. Programmers may have some incorrect assumptions whereas designing or implementing some functions. Due to this there are chances of having logical errors in the program. To detect and correct like logical errors procedural details require to be examined.

2. Certain assumptions on flow of control and data may lead programmer to make design errors. To uncover the errors on logical path, white box testing is must.

3. There may be definite typographical errors that remain undetected even after syntax and type checking mechanisms. Such errors can be uncovered during white box testing.