Should black box or white box testing be the emphasis for testers?

Question

Which type of testing would you say should be the emphasis (for testers/QAs), and why?

A quick set of definitions from wikipedia:

Black box testing

• takes an external perspective of the test object to derive test cases. These tests can be functional or non-functional, though usually functional. The test designer selects valid and invalid input and determines the correct output. There is no knowledge of the test object's internal structure.

White box testing

• uses an internal perspective of the system to design test cases based on internal structure. It requires programming skills to identify all paths through the software. The tester chooses test case inputs to exercise paths through the code and determines the appropriate outputs. In electrical hardware testing, every node in a circuit may be probed and measured; an example is in-circuit testing (ICT).

Just to clarify a bit more, I realize that both are important, but, usually, they are separate between dev and QA.

Is internal knowledge important for the tester/QA? I've heard arguments that testing with this knowledge in mind enables them to better test for problems, but I've also heard arguments that this knowledge can distract from functional needs and promote "testing to the code" rather than to the intended solution.

Answer 1

• Black box testing should be the emphasis for testers/QA.
• White box testing should be the emphasis for developers (i.e. unit tests).
• The other folks who answered this question seemed to have interpreted the question as Which is more important, white box testing or black box testing. I, too, believe that they are both important but you might want to check out this IEEE article which claims that white box testing is more important.

Answer 2

White Box Testing equals Software Unit Test. The developer or a development level tester (e.g. another developer) ensures that the code he has written is working properly according to the detailed level requirements before integrating it in the system.

Black Box Testing equals Integration Testing. The tester ensures that the system works according to the requirements on a functional level.

Both test approaches are equally important in my opinion.

A thorough unit test will catch defects in the development stage and not after the software has been integrated into the system. A system level black box test will ensure all software modules behave correctly when integrated together. A unit test in the development stage would not catch these defects since modules are usually developed independent from each other.