White box testing is a software testing technique that tests the internal structure and coding of software to verify the input-output flow and to improve the design, usability, and security of software.  Since the code is visible to testers, it is called a White box or Open box or Clear box testing. One can apply White Box testing at the unitintegration, and system levels of the software testing process.

In this blog, we cover why knowing the need of white box testing has been increasing, knowing what is white box, types of white boxes, techniques, and more.

Table of Contents:

Types of White Box Testing

Several testing types fall under White Box testing used to evaluate the usability of a software program.

Unit Testing:

Typically, Unit testing is one type of White box testing that is done on each unit of code as it is developed. It is done by the programmer. In this type, bugs are identified early on and hence are easier to fix. 

Testing for Memory Leaks:

It is yet another type that is extremely useful in slow-running applications, as memory leaks are responsible for slow-running applications.

White Box Penetration Testing:

In this type of testing, the tester has complete information, right from the application’s source code to the server that the application runs on. Thus it is easy to troubleshoot from various angles to identify security threats. 

White Box Mutation Testing:

It involves developing the best coding technique for expanding a software solution. 

Why do we need White Box testing?

We need White Box testing for: 

  1. Addressing broken paths in the coding processes.
  2. Addressing internal security leaks or holes
  3. Verifying the flow of specific inputs through the code.
  4. Conditional loop functionality
  5. Testing every function and statement individually.

In White Box testing, the working flow of an application is verified. A series of preset inputs are tested against expected outputs: when the expected output is not produced, there are bugs and those bugs are resolved.

Methods of White Box Testing include two important steps: understanding the source code and creating test cases and executing them. The tester should have a strong command over the application used in the coding as well as the security of the software. The tester looks for security issues and addresses them. Also, the source code is tested for proper flow and structure. This is done by writing more code. In this process, the developer usually creates small tests at each stage to check the flow for each of the series of processes.

Techniques of White Box Testing

Among the techniques of White box testing, Code Coverage Analysis is an important one. It helps identify those areas of a software program that are not exercised by test cases. Those untested parts are then tested by a code, thus raising the quality of the software.

Statement coverage requires every statement in the software to be tested at least once during the testing process. Branch coverage covers every possible path including loops in the software. 

There are other techniques such as Condition coverage, Multiple Condition coverage, control flow testing, and data flow testing.

How do you perform White Box testing?

Testers employing white box testing typically understand the source code and create test cases and execute. Understanding white box testing in software engineering involves a good working knowledge of the programming languages used in the software that is being tested. Besides, the tester should be aware of the secure coding practices as well, to identify security issues and prevent attacks. Also, the tester would develop tests for each process. This is often done by the developer as it requires a strong command over the code. Other methods employed are Manual Testing and trial and error testing.

Merits of White Box Testing:

  • Optimization of code by identifying hidden errors
  • Thorough testing as each path and statement are covered.
  • Testing can start even without the graphic user interface
  • Ease of automation is present in White Box testing.

Demerits of White Box testing:

  • It is complex, expensive, and time-consuming.
  • It requires a lot of detailing which if not performed can lead to production errors.
  • It requires professional resources and in-depth knowledge of the software.
  • It is detailed and each statement or path is covered. Unless one has adequate time and resources at hand, it cannot be performed successfully.


White box testing is complex on the one hand but thorough and detailed on the other. While small applications can be tested in minutes, larger applications may even take weeks to fully test. White box testing is done on software applications as they are being developed and once again after any modification.