Black, White, Grey box testing — differentiation and when to use it.

Black, White, Grey box testing — differentiation and when to use it.

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Whether we like it or not, software systems have become an integral part of life, from business applications to consumer products. And most people have had an experience with software that did not work as expected. Software that does not work correctly can lead to unwanted damages and problems including loss of business reputation, customers, time and even casualty if it’s a medical or mission critical application. As more and more businesses rely on income made digitally, that is why software testing is in high demand to assess the quality of the software and to reduce the risk of failure in operation.

One of common misconceptions of testing is that people think it only consists of running tests, i.e., executing the software and checking the results in excel sheet. On the contrary, software testing actually is a process which involves complex activities such as checking the test base itself off errors and test execution. The testing activities also stretch to things like test planning, analyzing, designing, and implementing tests, reporting and evaluating the quality of a test object.

Some testing does involve the execution of the component or system being tested; such testing is called dynamic testing. Other testing does not involve the execution of the component or system being tested; such testing is called static testing. Also, testing includes reviewing work products such as requirements, user stories, and source code. Despite another common misconception about testing that it focuses entirely on verification, it performs both verification and validation. For example, verification of requirements, user stories, or other specifications and validation checking whether the system will meet user and other stakeholder needs in its operational environment.

Now that we have baseline understanding on the testing concepts, this article compares different types of testing — Black, White and Gray Box.


BLACK BOX TESTING is defined as a testing technique in which functionality of the “Application Under Test” is tested without looking at the internal code structure, implementation details and knowledge of internal paths of the software.

In another words, with black box testing we solely focus on inputs and outputs of the software system without bothering about internal knowledge of the software program. So, the above black-box, object can be any software system you want to test. For Example, an operating system like Windows, a website like Google, a database like Oracle or even your own custom application.

This technique is useful when it comes to unit, integration, system and acceptance testing.


WHITE BOX TESTING is a method of software testing that tests internal structures or workings of an application, as opposed to its functionality like black box testing. It is also known as clear box testing, glass box testing, transparent box testing, and structural testing. In white box testing, an internal perspective of the system as well as programming skills are put to test and used to design test cases.

When developing a new digital product, it is almost mandatory to incorporate white box tests in your regular quality assurance routine. Basically, the tester chooses inputs to exercise paths through the code and determine the expected outputs. Therefore, white-box testing can be applied at the unit, integration and system levels of the software testing process.

Although traditional testers tended to think it is best being done at the unit level, it is used for integration and system testing more frequently today. It is because it can test paths within a unit, paths between units during integration, and between subsystems during system level test.

In order to avoid having errors appear in syntax or spelling, loop structures, code paths, implementation of code elements into a program, white-box testing is recommended with the following code coverage criteria:

· Control flow testing
· Data flow testing
· Branch testing
· Statement coverage
· Decision coverage
· Modified condition/decision coverage
· Prime path testing
· Path testing


GRAY BOX TESTING is a combination of white-box testing and black-box testing. The aim is to search for the defects if any due to improper structure or improper usage of applications.

As we know, in white box testing, understanding of the internal structure of the system is essential, but in black box testing this knowledge is not so necessary. How about in gray box testing? Under gray-box testing, testers should have partial understanding of the structure of the system relevant to the test as well as access to the database. Gray box testing is often used in integrated testing. However, based on algorithms and functions, it can also be used at various test levels.

I would like to note that gray box testing comes with a set of advantages because of various reasons, especially because of increasing needs for speedy and effective testing to satisfy current-day consumers that can be demanding. A lot of the modern-day web-based applications require effective testing because of high level of expectations for performance, as well as the amount of numerous data and functions being added on daily basis.

It is important to perform both grey box and black box testing in many cases for applications. And if there are a huge amount of errors found, a combination of grey box and black box testing helps in identifying problems and boosting performance.

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