When you hear the term “black box testing”, what’s the first picture that comes to your mind? Let me guess – a black box? Most likely, my guess is correct and you’re wondering how a black box relates to software testing. Well, to find out how they relate to each other and why this testing technique plays a relevant role in the software testing world, check out the following lines.
What is Black Box Testing?
In some ways, we’ve all done black box testing already in our daily lives. Take your car, for example. When you want to start your car, you press the start button and you expect the car to start. Or, if you’re old school, you put in the key and turn it 😉 Either way, you usually don’t have detailed knowledge of exactly what happens inside the car to get it started. The car is like a non-transparent box, that you don’t know the inner workings of. Like an actual black box, you can’t look through its outer shell and see what’s inside. This is also the basis for the concept of black box testing in software testing.
In this case, software is symbolically represented by the black box, as this testing technique focuses solely on the input and output of a software application. This implies that particular inputs go into the software program and result in certain outputs. If the actual output doesn’t match what was expected, a bug has been found. Using our car example, the input is illustrated as the press of the start button (or turning of the key) and the expected outcome is that the car starts up.
Black box tests are used to detect software errors caused by external factors. Using this testing approach, the software applications are tested from the perspective of the end-user, which involves testers to test the user interface of a digital product. You can imagine the user interface of a software as the outer casing of the black box. That’s the only part of the software that you see and thus, is tested. So, black box testing doesn’t check how the output is generated, but how the application behaves. By implication, this means the testers don’t know the inner workings of the application, such as code structure, implementation, or server logic. This is also the reason why black box tests don’t necessarily require any programming know-how of the testers.
To no surprise, black box testing is different to the opposite testing method, namely white box testing. There, the testers need to have a decent level of programming know-how, as they’re verifying the actual code of a software program. If you want to know more about white box testing and why it’s important in software development, check out our blog post White Box Testing.
Types of Black Box Testing
Generally speaking, there are several different types of black box testing. In order to give you a basic understanding, let’s focus on the three most common types that are fundamental in black box testing.
This type of black box testing is often the most commonly used one, as it covers the functional requirements and specifications of a software program. This testing type is vitally important since it concentrates on the core functions and menu operations of an application, as an example. The testers perform test cases, which cover certain actions and functions of the application by feeding the system with inputs, and then comparing them with the expected and actual outputs. This is essential, in order to detect bugs in the system and guarantee seamless use for your customers. To make sure your digital product’s functionality is working flawlessly, have a look at our functional testing methods that are part of our extensive quality assurance services.
In contrast to functional testing, non-functional testing doesn’t deal with particular functionalities of the software application. This type of black box testing focuses on non-functional aspects like usability, scalability, reliability, or performance of an application. Real end-users may experience critical issues while using your application that are not related to its functionality. This can negatively affect the user and customer experience, which is why non-functional testing is crucial for maintaining and improving the quality of your digital product. If you want to know more about taking your digital product to the next level with non-functional testing methods, check out our methods for usability testing and load/ performance testing.
Whenever there’s been changes to a software in terms of code fixes, system maintenance, or upgrades, regression testing ensures that new code modifications haven’t adversely affected existing functionalities of an application. This is necessary because every system change in your digital product can have unforeseen implications. Regardless of what kind of software application you have, regression testing should be a part of any development cycle. With 400,000 testers worldwide, our Crowd supports any digital product, so it’s worth having a look at our regression testing service.
How to Do Black Box Testing in Software Testing
Performing black box tests require you to follow a certain approach. The following list gives you an overview of the general steps that need to be performed:
- Examine and understand the requirements and specifications of the software application
- Identify valid and invalid inputs with expected outputs in order to check that the system detects them properly
- Create test cases with different test scenarios and inputs
- Execute the test cases
- Verify the expected outcomes with the actual outcomes
- Fix errors from failed test cases
- Retest the application to ensure fixed bugs are not recurring
Advantages of Black Box Testing
There are several benefits of black box testing:
- Black box testing is performed from the end-user’s perspective, so testers don’t need to have any technical background in terms of programming know-how or how the software is implemented.
- Both development and testing are separated from each other, which facilitates a more objective approach and helps reduce bias.
- Test cases and test scenarios can already be created once the software requirements and specifications are defined.
Disadvantages of Black Box Testing
Considering the advantages of black box testing, there are also some downsides:
- There are limitations to the number of possible inputs that can be verified, as a thorough testing procedure of the entire software program can be quite drawn-out.
- Black box testing can be redundant if the development or design team have already conducted tests.
- As black box tests depend on software requirements and specifications, they must be clearly defined in advance. Otherwise, the test case creation becomes extremely challenging.
What Are Some Simple Examples of Black Box Testing?
As already introduced in the beginning, the term “black box” can represent a type of software. This can be a mobile application (like Instagram), a website (like testbirds.com), a database (like Oracle), or an operating system (like macOS) – just to name a few. To give you a better understanding of this testing method and what it can look like in real life, let’s use this simplified black box testing example to illustrate:
The test object is a mobile application with a personal user account. In order for users to gain access to it, they need to authorize themselves through a simple login screen. Two required fields need to be filled by the user – a username and a corresponding password. Subsequently, the input and output are defined as the following values:
Input: username, password
Output: access to personal user account
Considering a tester performing the following inputs with the corresponding expected outputs, both inputs are valid in terms of the actual results:
If a tester experiences a different actual result than the expected output, a bug has been discovered:
As you now know, we’ve all done black box testing already, in some way or another. For software, this testing technique plays a crucial role in testing digital products from the end-users point of view, in order to guarantee a flawless user experience. Black box testing aims to test the user interface without considering any code-specific knowledge. The testers perform inputs and validate the actual outputs against what was expected. Performing black box tests allow you to not only focus on quality assurance and the functional testing perspective, but it can also cover non-functional testing such as usability. Find out more about how Testbirds can help you – with its 400,000 testers worldwide – to perform functional, as well as non-functional black box tests!
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About the author
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 technolo