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White Box Testing

White Box Testing

30 July 2022 10 MIN READ BY Rajesh K

What is White Box Testing

White box testing technique evaluates the working of an application software by testing the functioning of its source code and its internal structure.

  • The software testers can access or see the source code and need to test it. So, programming knowledge or skills are inevitable for software testers.
  • We test every line of the source code here, which ultimately leads to inspecting the inner workings of the entire software system.
  • Software developers also do white box testing as this involves software testing of the functioning, structure and working flow of the source code. Software developers do this mostly after
    • Fixing a bug, or
    • After the completion of a new functionality or feature or a module, and
    • Before submitting the changes for further testing by the software testers.


Advantages of White Box Testing

We can briefly summarize the advantages of white box testing as follows,

  • Very meticulous as it tests the entire source code and structure —> The transparency of the internal code structure is beneficial as it helps to identify the type of input data needed for testing.
  • White box testing results in code optimization, where it removes error-prone and unnecessary or insignificant lines of code.
  • Teams can start this type of testing at an earlier stage without waiting for the completion of development.
  • The test cases for white box testing are easy to automate.
  • Communication burden between software developers and software testers gets reduced as software testers performing white box testing are expected to possess knowledge in programming languages and skills.


White Box Testing Process

White box testing begins by scrutinizing and understanding the source code, its design and structure, corresponding to the application software to be tested, so that proper test cases can be created.

1. Familiarizing the Source code:-
  • The software tester should familiarize with the internal source code, its structure and its process flow.
    “The tester should also be well versed with the programming language used to develop the application.”
  • We should understand the different functionalities embedded in the application through its source code. This will be helpful in identifying and creating different test cases for testing the application.
  • The tester should be aware of secure coding practices as security is a major concern while testing an application.
2. Make Test Cases and Execute them:-
  • Test cases for each process in the application software to be tested are created and executed by the software tester either manually or after automating it through scripts.
  • We create and execute test cases for every single path in the working flow of the source code.
  • We analyze and record the results after executing the test cases.


Testvox - Software Testing Service


Types of White Box Testing

White Box testing utilizes different testing types to evaluate an application software.

i. Unit Testing:-
  • Tests a Unit, which is the smallest block of code that can be logically used for a purpose. Unit testing ensures the proper functioning of each component of the source code as intended.
ii. Mutation Testing:-

Based on modifications or mutations made to the source code to examine if the test cases executed can reveal bugs in the code.

  • If all the test cases fail, then the source code tested is working perfectly.
  • If any of the test cases passes the test, it signifies an error or bug in the source code
iii. Integration Testing:-
    Intended to check the combined working of different Units/Modules/Components of the application’s source code.

  • Ensures that the modules that worked correctly independently are also working fine when combined.
    “The purpose of this type of testing is to expose any errors in the interaction of different units when associated together.”


White Box Testing techniques

White box testing aims to scrutinize the source code of an application software comprehensively

1. Code Coverage Analysis:-
  • It identifies areas of a program that the set of test cases created and executed have not yet tested. After identifying these gaps, we create further test cases to test and verify the untried parts of the code.
The most popular white box testing techniques related to Code Coverage are Statement Coverage, Branch Coverage, Path Coverage, Function Coverage, Condition Coverage and Multiple Condition Coverage.
2. Statement Coverage:-
  • It ensures that we execute and test all executable statements of the source code of an application software at least once.
  • It finds branch instructions or other executable statements that the system does not execute or use, and identifies dead codes.
    Statement coverage = (Number of statements executed/Total number of statements)*100.
3. Branch Coverage:-
  • The software tester identifies all conditional and unconditional branches and ensures that they execute and test each branch operation at least once. We test every possible branch within an application here.
Branch coverage = (Number of executed branches/Total number of branches)*100.
4. Path Coverage:-
  • We execute and test all possible paths covering each executable statement and branch instruction at least once. To achieve this, we need to understand the control flow of the source code well.
  • It assures that we examine all program paths at least once.
  • We can identify broken paths and redundant paths using this testing.
Path Coverage = (Number of paths traversed/Total number of paths in the program)*100.
5. Function Coverage:-
  • Evaluates the defined functions within the source code. We pass the required input parameters to these functions to examine if the working of each function is logical as intended.
6. Condition Coverage:-
  • Evaluates the variables or expressions in a conditional statement. We evaluate and test the end result of each logical condition here.
7. Multiple condition coverage:-
  • We evaluate all the different combinations of the possible outcomes of conditions to make a decision.



The size of the application software being tested determines the ease and speed with which we can execute white box testing. We can test small applications quickly, but large applications may require more time.

  • Since we conduct testing through the source code of the application, we can identify maximum structural loopholes and bugs at a profound level.
  • Software developers and QA personnel can bring greater efficiency, accuracy, and cost-effectiveness to white box testing through its automation.
  • Because we can automate white box tests, we can execute them in CI pipelines to provide faster feedback for the software developers when evaluating the source code.
  • The software industry widely uses white box testing, especially for applications dealing with high risk or critical business.

Rajesh K

Possessing Post Graduation in Applied Electronics with a specialization in Microprocessors and embedded systems, I started my career as a faculty in computer applications. Shifted to IT industry after few years and worked as a Quality Analyst for almost 7 years.