How To Effectively Perform White Box Testing

Timothy Joseph
Timothy Joseph | August 11, 2021
How To Effectively Perform White Box Testing

White box testing is a type of testing technique that aims to evaluate the code, design and the internal structure of a program to improve its design, usability and security. It is one of the two parts of Box Testing methodologies included in software QA testing.

The term “white box” is used to refer to the concept of the see-through box. Simply put, the clear box, or White Box symbolizes the ability to look through the outer shell of a program and into its inner layout.

In this guide, we’ll discuss everything you need to know about white box testing, how it is done, its pros and cons, and the best tools available to do it.


What Does White Box Testing Focus On?

When white box tests are carried out correctly, they can identify the following issues and concerns in the code of an application:

  • Security Gaps and Vulnerabilities: White box testing techniques can inspect the code to see if the best security practices have been applied when creating the application. It also analyzes the code to see if it is vulnerable to known threats and security attacks.
  • Expected Output: This type of testing applies all potential inputs to certain functions to see if the expected result is always the same.
  • Poorly Structured or Broken Paths: White box testing helps to assess and identify if the conditional logic of the application is inefficient, broken, or redundant.
  • Loop Testing: The testing method helps to ensure that single loops, nested loops, and concatenated loops are efficient. Correct handling of local and global variables as well as the conditional logic is analyzed.
  • Data Flow Testing (DFT): It helps to monitor variables as well as their values as they go through the code to identify ones that have not been appropriately initialized. It also checks if variables are incorrectly manipulated and declared but never used.


How To Perform White Box Testing

To provide you with a simple explanation of how experts perform white box testing, we will talk about the process in two steps.

The following are the primary tasks testers do when applying the white box testing approach:

  1. Understand the Source Code

    One of the first things testers will do is study and understand a program’s source code. Since the inner workings of a software application are being tested in white box testing, these testers need to be highly experienced in the various programming languages as well as secure coding practices.

    Since security is one of the main goals in testing software, testing experts should be able to identify security concerns to prevent attacks from cybercriminals and users who may accidentally insert malicious code into the program without knowing.

  2. Create Test Cases and Execute

    The next step involves testing the source code of an application to see if its flow and structure work properly. One way testers perform this is by writing additional code so they can test the program’s source code.

    Testers develop minor tests for every process or series of processes within the app. This step requires testers to have in-depth knowledge of the code, which is why it is usually performed by the developer.


White Box Testing Techniques

The following are the most popular techniques used in white box testing:

  • Code Coverage

    One of the primary objectives of white box testing is to make sure that the source code is covered as comprehensively as possible. That is why the metric code coverage is used as it shows how much of a program’s code has tests to check its functionality.

    Using code coverage allows testers to verify how much logic is actually being executed and tested using the unit test suite for a given application.

  • Branch Coverage

    In branch coverage, testers map the code into different branches of conditional logic. This is done to make sure that each of these branches is covered by the unit tests.

    The tester identifies all unconditional and conditional branches in a branch coverage approach and then writes the code to execute as many of these branches as they can.

  • Path Coverage

    The path coverage approach concerns itself with the linearly independent paths present in the code. A tester maps out the code’s control flow diagram which is then used to design the tests in this technique.

    The tester also writes unit tests and executes as many of them as possible and uses the control flow of the program to achieve this. The main goal here is to identify any inefficient, redundant, or broken paths.

  • Statement Coverage

    Lastly, statement coverage is a technique in white box testing that ensures every executable statement in the code is run and tested at least once.

    The goal of statement coverage is to help identify unused branches, unused statements, dead codes, and missing statements.


Types of White Box Testing

There are several testing types in white box testing that are used to evaluate the usability of a program, software package, or block of code.

  • Unit Testing: Often the first type of testing performed, unit testing is carried out on each block of code or unit as they are developed.
  • Memory Leak Testing: A tester tests the application for memory leaks, which is one of the main causes for slow-running programs.
  • White Box Mutation Testing: This type of testing is used to identify the best coding techniques for use in increasing the capabilities of a software program.
  • White Box Penetration Testing: This test aims to attack the program code from various angles to expose any gaps and threats in its security.
  • Static Code Analysis: This test automatically identifies coding errors and vulnerabilities in the static code.

Black Box vs. White Box Testing

As stated earlier, white box testing and black box testing are two different methods of application testing. Here are the differences between the two:

Parameter Black Box Testing White Box Testing
Black box testing is a testing approach that tests the software without knowing its internal structure. The main focus here is the end-user experience
White box testers know the internal coding of the program
The main objective of this kind of testing is to check the functionality of the system under test
White box testing ensures that the code quality is up to standard
Base of testing
In black box testing, the testing is based on external expectations
Internal programming of a software is known in white box testing
Black box testing is great for higher levels of testing such as in acceptance and system testing
White box testing is ideal for a lower level of testing such as integration and unit testing
Testing Method
Black box testing is based on trial and error
White box testing can look into data domains and internal boundaries
Programming Knowledge
Black box testing does not require any programming knowledge
Programming knowledge is required to perform white box testing
It is less exhaustive and time consuming
It is very exhaustive and time consuming
It is well-suited for large code segments
It helps to remove all extra lines of code, that might give rise to extra defects
It becomes necessary to update the automated test script with every modification to the application
Automated test cases become redundant if there are frequent changes made to the code

Advantages of White Box Testing

  • Helps in code optimization

  • Can be easily automated

  • Testing is thorough

  • Testing can start early in the SDLC phase

Disadvantages of White Box Testing

  • Can be complex and expensive
  • Developers running white box tests are often not detail-oriented, which can lead to production delays
  • It requires professional resources such as understanding of the programming language

White Box Testing Tools

Here are some of the most popular tools used in white box testing:

  • Parasoft Jtest: This integrated Java testing tool lets users meet development cycles while ensuring the quality of the code. Its set of tools allow users to identify defects in coding at every stage of the software development process.
  • NUnit: This is a unit-testing framework intended for all .net languages. It was initially ported from JUnit but has been fully rewritten with numerous features and support for different .net platforms.
  • HTMLUnit: This GUI-less browser for Java apps model HTML documents while providing an API that lets users invoke pages, click links, fill out forms, and more.
  • PyUnit: This is a Python port of JUnit that incorporates five key classes in its unit test module.
  • CppUnit: CppUnit is a C++ port of the well-known JUnit framework that is used for unit testing.


White box testing is a complex testing procedure that requires testers to have in-depth knowledge of the application’s code. Compared to black box testing, white box testing focuses on the inner workings of the software program being tested.

The information in this guide should help give you a better idea of what white box testing is about and its importance in the quality assurance process. Partnering with QASource for white box testing ensures that you get a high-quality, affordable, and reliable experience. Get in touch today!


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