White Box Testing – An Indispensable Testing Method

by | Mar 6, 2020 | Terms from the world of IT explained, Crowdtesting, Usability & User Experience | 0 comments

When was the last time you had an issue with your car? Could you fix it yourself or did you need the help of a mechanic? If it wasn’t a simple fix, you probably relied on a mechanic, who checked the engine and inner workings of your car to find the defect and fix it at its root. 

Now you might be surprised why I’m talking about your car and mechanics. How is this related to white box testing? The reason is more obvious than you’d think. In its essence, the work of a mechanic can be compared with how white box testing works. In the software testing world, white box testing is a commonly used testing method which is why it’s worth taking a closer look at.

What is White Box Testing?

When you hear the term “white box testing”, you might wonder what a plain white box has to do with software testing. In fact, they are related – at least symbolically. A physical white box allows you to look through to its core since it’s a transparent object. If you look at it from the perspective of software testing, the white box represents the software product for which the code is the core.

Taking the real-life example from the introduction, both the work of a mechanic as well as white box testing aim to look past the outer shell of a product’s user interface. While the mechanic checks the inner workings of a car, white box testing involves testers who look at the source code of a software application and review it. Usually, these testers will be developers or professional software testers with a certain level of programming know-how.

Each line of code serves the purpose of executing a certain command and subsequently needs to be checked to see if the commands are executed correctly. Testers check and set up test cases that cover the code structure as well as the functionality of an application.

Since the testers revise the code of an application, white box testing is also known as code-based testing. However, you might also have heard the synonyms glass box testing, clear box testing, or transparent box testing.

Black Box Testing

The opposite method to white box testing is black box testing. Similarly, this term is symbolic of a black box, where you can’t look through to its core but only see the outer shell. The difference between black and white box testing is that black box testing only gives you the opportunity to see the user interface of a software application, but not the inner workings. This means that testers test the user interface of your product and these testers are usually also the target group of your product.

User experience and usability are decisive factors for the success of your applications. If you want to know more about how you can use Crowdtesting to improve your digital products, have a look at our usability and UX testing services.

What Are the Reasons for Performing White Box Tests?

When developing a new digital product, it’s essential to incorporate white box tests in your regular quality assurance (QA) routine. One of the fundamental objectives of this testing method is to review various code sequences for a software application. For this process, designing test cases that cover the entire software code are required. In doing so, every code path needs to be run individually at least once, and the internal security of the software has to be verified as well. White box testing helps you identify bugs in the code, which prevent your software from working flawlessly. These bugs may occur as errors in:

  • Syntax or spelling
  • Loop structures
  • Code paths
  • Implementation of code elements into a program

Advantages of White Box Testing

There are several advantages of white box testing:

  • It’s a very thorough testing approach, as it usually covers the entire code of a software
  • White box testing helps improve the code by identifying and removing hidden bugs as well as keeping the code structure clean
  • Testing can already be initiated at an early stage of development, as no end-user interface is needed
  • Test cases can be easily automated

Disadvantages of White Box Testing

Besides all the advantages that come along with white box testing, there are (unfortunately) also some downsides:

  • It’s a complex and sometimes costly testing method
  • Testers are expected to have detailed knowledge about programming, as they need a deeper understanding of the code
  • When developing on a large scale, it becomes quite time-consuming
  • Changing and restructuring the code prompts new test cases that need to be re-designed and run again

As you can tell (and see in the picture below 😉 ), white box testing has solid arguments on the table. Even if you consider the potential downsides, it’s one of the best testing methods to detect bugs in a system even at an early stage in the development life cycle.

An Easy Example of White Box Testing

White box testing aims to define certain inputs before a test runs, verify them, and subsequently compare the actual outcomes with the expected results. If the expected results do not match the corresponding inputs, you‘ve discovered a bug.

By using a quite simplified code example, I’ll demonstrate what white box testing might look like. As a starting point, we assume the following code section:

INPUT = X & YHere you define the input for X and Y – Let’s say X=90 and Y=120
RESULT (Z) = X + YThis line is specified as the result of X + Y. When X=90 and Y=120, the sum Z is 210
IF (RESULT (Z) > 200)In this line, we verify if the result Z > 200. In this case, the condition proves to be true
(“Positive”, RESULT)   
(“Negative”, RESULT)
By determining different values for X and Y, and exercising the statements of the code, you can review if the source code is correct.

Are You Running White Box Tests?

White box testing is a vital testing method in the development of a digital product. Every code path and function is verified on potential bugs in the system as well as its security. Depending on the tested software, white box tests can be quite time-consuming and complex. Nevertheless, these testing techniques are commonly used in software development since they ensure proper code functionality and are essential in quality assurance. To make sure that you also cover the front-end QA testing, check out our Crowdtesting QA methods. Make use of our 400,000 testers worldwide and let them hunt down potential errors in your digital product.


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About the author

Christian Putz

Christian Putz


When Christian is not striving for new personal bests with Freeletics, he is getting an overview at Testbirds as a trainee and explores all departments.


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Testbirds specialises in the testing of software such as apps, websites and Internet of Things applications by using innovative technologies and solutions. Under the slogan, “Testing Reality”, the company offers various testing methods to its clients looking to optimise the user-friendliness and functionality of their digital products. With over 250,000 registered testers located in 193 countries, Testbirds is one of the world’s leading crowdtesting providers. In addition, the IT service provider utilises cloud based technologies to support customers in the optimisation of their digital products. The combination of the two testing methods delivers a unique and extensive portfolio that takes the quality of software to the next level. Testbirds was founded in 2011 by Philipp Benkler, Georg Hansbauer and Markus Steinhauser. Today, the company has over 100 employees. Other than its headquarters in Munich, there are now offices in Amsterdam, London and Stockholm, franchises in Hungary and Russia and sales partners in Italy.

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