Suppose you are a manufacturer looking to introduce a new electric kettle. Your product team develops it and releases it in the market without checking to make sure it is not faulty. A customer plugs it in and the kettle malfunctions. The complaints pile up. So what do you do? Before re-launching the kettle, you will make sure to “test” it.
In the same way, web and mobile applications need to be tested before deployment to make sure they are error-free and work as expected. Black box and white box testing are the two main types of software testing that prove helpful here.
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Software testing does not have to be an isolated phase of the software development life cycle. It needs to be done at various stages of SDLC. An app can be tested for accuracy and correctness right from the design and prototyping stage up until the moment right before launch.
What Is Black Box Testing?
Black box testing refers to a type of software testing process that requires the tester to test an application without possessing any knowledge of the application’s internal structure. The application that is being tested can be thought of as a black box that they cannot see inside. However, they do not go in completely blind.
Black box testers are informed about the expected behaviour of the software. Instead of worrying about the technologies that have been used to put together and develop the app, the tester focuses on whether or not the app meets all the requirements listed in the Software Requirements Specification (SRS). With the help of a user interface, they can check the various features in the app and see whether each of those features is performing its designated function(s).
Testers are supposed to make sure that the app is carrying out all its functions not just correctly but also efficiently. There may be certain non-functional requirements that need to be met, such as data security or the interface’s ease of use.
It seems pretty simple, doesn’t it? Well, it is not! The tester needs to know how to carefully determine what test cases to run based on the specified requirements, and then analyse the outcomes obtained.
Black box testing is also known as:
- Specification-based testing
- Behavioural testing
- Data-driven testing
- Input-output testing
No matter what stage of testing you are at (unit testing, acceptance testing, or anything in between), you can perform black box testing at any point.
What Is White Box Testing?
White box testing refers to a type of software testing process that requires the tester to possess in-depth knowledge of the internal code structure of the application that they are testing. The tester needs to not only ensure that the app is functioning correctly but also know how the app is performing its functions.
Compared to black box testing, white box testing is done at a much lower level. Often, only those who have worked on the code for a particular application are able to test it thoroughly. This includes the developers and technical engineers who are aware of the internal structure and technologies used in the development process. This is because they should be able to thoroughly understand what goes on behind each feature or functionality present in the app. The inputs that they choose for conducting the tests need to be based on their knowledge of the app’s internal design and structure.
White box testing helps to determine and confirm the correctness of each and every path that the app takes when fed different kinds of inputs.
Due to the transparent nature of the testing process where the tester needs to be able to see beyond the app’s surface-level operation, white box testing is sometimes also referred to as clear-, glass-, transparent-, or open-box testing. Other names include:
- Code-based testing
- Logic-coverage or logic-driven testing
- Structure-based or structural testing
While white box testing is usually performed on the lowest level i.e. unit testing, it can also be applied to integration or system testing.
What Is the Difference Between Black Box and White Box Testing?
A brief comparison of white box and black box testing can be drawn with the help of the following example:
Suppose your fridge is causing you problems. Everything that you store in it becomes soggy due to condensation. Now, you know this is unexpected behaviour, so something is definitely wrong. To test the fridge, you try adjusting temperature and other settings, but you continue to face the same issue: condensation. You decide to call someone from the fridge company so they can come over and see what is causing the issue. The expert that the company sends picks up the fridge, takes it apart for inspection and finds out where the fault was. In this case, you could say that you performed black box testing and the specialist acted as a white box tester.
There are many other differences between black box and white box testing. They are summarised in the table below.
Black Box Testing | White Box Testing |
| It does not require the tester to have knowledge of the internal structure of the application. | It requires the tester to have knowledge of the internal structure of the application. |
| The tester does not need to possess programming skills. Thus, even an end-user can perform it. | The tester must possess programming knowledge. Thus, only developers or testers with coding knowledge can perform it. |
| It is performed from the perspective of the end-user. | It is performed from the perspective of the coder. |
| It focuses on ensuring that the software is performing its functions correctly, producing outputs that match expected outcomes. | It focuses on the accuracy and efficiency of the code and its structure. |
| Test cases are written on the basis of what is specified in the SRS. | Test cases are written on the basis of the Detailed Design Document. |
| It is not a very extensive process, hence it does not take a lot of time and may not produce very detailed reports. | It can take a lot of time since it revolves around performing exhaustive tests and generates highly detailed reports. |
| Due to the simplicity of the testing process as well as the need to make sure that the app is fit for human use, it is preferred that this type of testing is performed manually. | Since this process could turn out to be very time-consuming, especially for larger projects, it might be necessary to use certain testing and automation tools. However, it can be performed manually too. |
| It is most appropriate for higher levels of testing, such as acceptance testing. | It is most appropriate for lower levels of testing, such as unit testing. |
| Lots of trial-and-error is involved in this type of testing since the tester is clueless about the software’s internal operation. | Since the app’s internal structure is known to the tester, they can adopt a testing strategy that could (but should not!) break the app. |
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Final Thoughts
If software applications are released to the end-users without being tested properly, it can cause serious harm. It might leave the users utterly helpless and frustrated if they run into unexpected errors or faults, causing the developers to end up with negative reviews.
Thus, software quality assurance engineers and testers must perform due diligence before implementing new apps. Whether it is a web-based application or a native or hybrid mobile app development project, black box and white box testing must be part of every software application’s testing phase. The better their testing design and plan, the easier it will be to catch bugs early on, the better the application will perform, and the less likely it will be to cause problems for end-users.
