Explain Black box and White box testing? What are their advantages and disadvantages?

For complete testing of a software product both black and white box testing are necessary.

Black-box testing
This testing looks at the available inputs for an application and the expected outputs that should result from each input. It does not have any relation with the inner workings of the application, the process undertaken or any other internal aspect of the application. Search engine is a very good example of a black box system. We enter the text that we want to search, by pressing “search” we get the results. Here we are not aware of the actual process that has been implemented to get the results. We simply provide the input and get the results.

White-box testing
This testing looks into the complex inner working of the application; it tests the processes undertaken and other internal aspects of the application. While black box testing is mainly concerned with the inputs and outputs of the application, white box testing help us to see beyond i.e. inside the application. White-box testing requires a degree of sophistication which is not the case with the black-box testing, as the tester is required to interact with the objects that are used to develop an application rather than having easy access to the user interface. In-circuit testing is a good example of a white-box system testing where the tester is looking at the interconnections between different components of the application and verifying the proper functioning of each internal connection. We can also consider the example of an auto-mechanic who takes care of the inner workings of a vehicle to ensure that all the components are working correctly to ensure the proper functioning of the vehicle.

The basic difference between black-box and white-box testing is the areas of focus which they choose. We can simply say that black-box testing is focused on results. Where if an action is performed and the desired result is obtained then the process that has actually been used is irrelevant. White-box testing, on the other hand focuses on the internal working of an application and it is considered to be complete only when all the components are tested for proper functioning.

Advantages of Black-box testing
- Since tester does not have to focus on the inner working of an application, creating test cases is easier.
- Test case development is faster as tester need not to spend time on identifying the inner processes; his only focus is on the various paths that a user may take through GUI.
- It is simple to use as it focuses only on valid and invalid inputs and ensures that correct outputs are obtained.

Drawbacks of Black-box testing
Constantly changing GUI makes script maintenance difficult as the input may also be changing. Interacting with GUI may result in making the test script fragile and it may not properly execute consistently.

Advantages of White-box testing
- Since the focus is on the inner working the tester can identify objects pro grammatically. This can be useful when the GUI is frequently changing.
- It can improve stability and re usability of test cases provided the object of an application remains the same.
- By testing each path completely it is possible for a tester to achieve thoroughness.

Drawbacks of White-box testing
Developing test cases for white-box testing involves high degree of complexity therefore it requires highly skilled people to develop the test cases. Although to a great extent fragility is overcome in white-box testing BUT change in the objects name may lead to breaking of the test script.