White Box Testing

White box testing (WBT) is also called Structural or Glass box testing. White box testing involves looking at the structure of the code. When you know the internal structure of a product, tests can be conducted to ensure that the internal operations performed according to the specification. And all internal components have been adequately exercised.
White Box Testing is coverage of the specification in the code.

Code coverage:
Segment coverage:
Ensure that each code statement is executed once.

Branch Coverage or Node Testing:
Coverage of each code branch in from all possible was.

Compound Condition Coverage:
For multiple condition test each condition with multiple paths and combination of different path to reach that condition.

Basis Path Testing:
Each independent path in the code is taken for testing.

Data Flow Testing (DFT):
In this approach you track the specific variables through each possible calculation, thus defining the set of intermediate paths through the code.DFT tends to reflect dependencies but it is mainly through sequences of data manipulation. In short each data variable is tracked and its use is verified.
This approach tends to uncover bugs like variables used but not initialize, or declared but not used, and so on.

Path Testing:
Path testing is where all possible paths through the code are defined and covered. Its a time consuming task.

Loop Testing:
These strategies relate to testing single loops, concatenated loops, and nested loops. Independent and dependent code loops and values are tested by this approach.

Why we do White Box Testing?
To ensure:

• That all independent paths within a module have been exercised at least once.
• All logical decisions verified on their true and false values.
• All loops executed at their boundaries and within their operational bounds internal data structures validity.

Need of White Box Testing?
To discover the following types of bugs:

• Logical error tend to creep into our work when we design and implement functions, conditions or controls that are out of the program
• The design errors due to difference between logical flow of the program and the actual implementation
• Typographical errors and syntax checking

Skills Required:
We need to write test cases that ensure the complete coverage of the program logic.
For this we need to know the program well i.e. We should know the specification and the code to be tested. Knowledge of programming languages and logic.

Limitations of WBT:
Not possible for testing each and every path of the loops in program. This means exhaustive testing is impossible for large systems.
This does not mean that WBT is not effective. By selecting important logical paths and data structure for testing is practically possible and effective.

Types of testing under White/Glass Box Testing Strategy:

Unit Testing:
The developer carries out unit testing in order to check if the particular module or unit of code is working fine. The Unit Testing comes at the very basic level as it is carried out as and when the unit of the code is developed or a particular functionality is built.

Static and dynamic Analysis:
Static analysis involves going through the code in order to find out any possible defect in the code. Dynamic analysis involves executing the code and analyzing the output.

Statement Coverage:
In this type of testing the code is executed in such a manner that every statement of the application is executed at least once. It helps in assuring that all the statements execute without any side effect.

Branch Coverage:
No software application can be written in a continuous mode of coding, at some point we need to branch out the code in order to perform a particular functionality. Branch coverage testing helps in validating of all the branches in the code and making sure that no branching leads to abnormal behavior of the application.

Security Testing:
Security Testing is carried out in order to find out how well the system can protect itself from unauthorized access, hacking – cracking, any code damage etc. which deals with the code of application. This type of testing needs sophisticated testing techniques.

Mutation Testing:
A kind of testing in which, the application is tested for the code that was modified after fixing a particular bug/defect. It also helps in finding out which code and which strategy of coding can help in developing the functionality effectively.

Besides all the testing types given above, there are some more types which fall under both Black box and White box testing strategies such as: Functional testing (which deals with the code in order to check its functional performance), Incremental integration testing (which deals with the testing of newly added code in the application), Performance and Load testing (which helps in finding out how the particular code manages resources and give performance etc.) etc.