White Box Testing and Black Box Testing

Friday, 20 January, 2017

On a daily basis, people interact with different variations of software. Using applications on smartphones, some desktop application or approaching a certain web page through the browser – it is all software usage. Behind every software, there are several series of software testing.

Software testing is the process of verifying that the application meets the user’s expectations. Software testing methodologies are the different ways of ensuring that application is thoroughly tested and that the product is fit for release. These approaches involve testing to assure that the product works by its requirements so that there won’t be any undesirable side-effects after its release and that in the worst-case scenario the software will not fail. Software testing methodologies get more complex the larger the number of different platforms and devices that need to get tested. Software companies bring several various methods of software testing. There are two main categories – White box testing and Black box testing.
In this article, we will discuss White box testing and Black box testing, explore the advantages and disadvantages of each and compare them to see when is the most appropriate time to use them.

White Box Testing

White box testing is the software testing method where internal structure is known to the tester who is going to test the software. White box testing is also called glass box testing, open box testing, transparent box testing, structural testing, and clear box testing. All of these terms indicate that internal mechanisms are visible to testers. In white box testing, it is all about testing internal coding and infrastructure of software. White box testing is a methodology used to validate the internal framework, components, mechanisms and objects and of an application.

First, the code is verified according to documented specifications. When the tester is completely familiar with the internal structure of the code, then tests can be run to check if the system meets requirements listed in the specification document. This testing focuses on boosting security, improving the flow of inputs and outputs and on improving usability and design. It uncovers application vulnerabilities. This type of testing is the best method to find out errors in the early stage of software development life cycle.

Here, producing the test cases is the most important part. For this, testers need to have certain knowledge about programming code. These test cases will be executed on every line of the code, and they will detect all possible anomalies. It is important, of course, that testers exactly know what the program is supposed to do. Only then do they determine if a program diverges from its intended goal.

Black Box Testing

Black box testing is the software testing method which is used to test software, but in the way that testers know nothing about the internal workings of the application. That is the reason why the method is named Black box testing because the tester is blind to everything inside the tested software. The internal code structure, paths of the software and implementation details are not a concern for the tester who is performing Black box testing. The behaviour of the application’s functions is all that is tested here. That is the reason why Black box testing is also known as functional testing – it tests the functionality of a program. Except functional testing, there is also non-functional Black box testing, which tests how long it takes to process the data and generate outputs or how long it needs for a function to respond to user’s inputs. So, Black box testing collects data and compares them with the expected results. This type of testing is based on the software requirements and specifications.

The Black box testing method is what most of the testers perform in the practical life. All testing is done from the user’s point of view because a tester only knows what the application is supposed to do, not how will it do it. Only end-user experience can be tested. Testers pass valid and invalid inputs and determine the correct expected outputs. All the test cases are based on requirements and specifications document. The primary goal of Black box testing is to determine if the software is working as expected and if it is meeting the user expectations. Any Black box testing can be performed in a few steps:

Differences Between White Box Testing and Black Box Testing

Often people get confused about software testing terminology, about who is responsible for performing which type of a test, when the tests are performed and what inputs are required to carry out different types of testing. We will discuss the main differences between White box and Black box testing.

The main difference between White and Black box testing is that in White box testing internal structure is being known to the tester who is going to test the software, while in the Black box the tester checks the software without knowing the inner structure of code or a program. Developers carry out White box testing, while Black box testing carries testers. Black Box testing starts when Requirement Specifications documents are delivered, but White box testing can begin based on the Detail Design documents. Implementation knowledge and programming are not required in Black box testing, while in White box testing they are. That is because behaviour testing, functional testing, and close box testing are carried out under Black box testing, while logic testing, structural testing, loop testing, path testing, code coverage testing and open box testing are done under the White box testing.

Black box testing concentrates on the functionality of a system. White box testing focuses on the program code of a system, like structure, conditions, branches, loops, etc. Black box testing means external testing or functional tests, and White box testing means internal testing or structural test. The primary goal of Black box testing is to check what functionality is performing by the system under test, while the main aim of White box testing is to check how the system is performing.

The question arises, which testing method is more important – White box testing or Black box testing? Both of them are equally important, depending on their contribution to the level at which they are implemented. White box testing is important at the beginning of software development because it can catch defects early in the development stage. This method prevents a small problem from becoming a crucial error after the code is integrated into the main system. On the other hand, Black box testing ensures that all the different software modules work well together after being integrated. One is sure; both testing techniques are required for successful software delivery.

Advantages and Disadvantages

The advantages of White box testing include:

The disadvantages of White box testing include:

The advantages of Black box testing include:

The disadvantages of Black box testing include:


Software testing is an important part of software development cycle, and many types of testings can be performed. They are separated into two main types – White box testing and Black box testing. White box testing is a testing approach that considers the internal mechanism of a system. Black box testing is a testing approach that ignores the internal mechanism of a system. White box testing is often used for verification, and Black box testing is often used for validation. White box testing is based on the inside workings of an application, while Black box testing involves testing from an end-user type perspective.

There are many advantages and disadvantages of both of the approaches, but they are equally important in the process of bringing quality and error-free product on the market. For complete software examination, they are both required. With selecting a test methodology, testers need to be flexible and change approach considering priority and resources.

Ana Lozančić

Ana is a content Marketing specialist and blogger. She graduated in Faculty of humanities and social sciences. She enjoys learning and applying knowledge about marketing and social media, covering latest trends and topics about software development subjects.


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