Black Box vs White Box Testing: Do You Need Both?

Software testing is a science full of specific terms and classifications. Black box and white box testing are among them. QA specialists run tests with a clear understanding of how a program or an individual feature has to perform. However, there are two ways this process may go.

Usually, a testing specialist from an outsourced QA company doesn’t have access to code and doesn’t know how features work on the backend. They perform black box testing, interacting with functionalities via frontend while everything “in the box” remains secret. The opposite approach, white box testing, implies full access to everything in the app. A QA engineer can test an app mimicking real user behavior or “look inside” the secret “box” if needed.

So let’s take a closer look at these types of testing and learn more about their particularities.

What Is Black Box Testing?

As you’ve already understood, black box testing means running a quality check without knowledge of architecture or access to the code of a product under test. A QA specialist doesn’t need this information. Instead of the backend technologies, they focus on the requirements described in the technical documentation. Hence, QA engineers check only the final product, not underlying technologies.

What Is White Box Testing?

White box testing, on the contrary, implies that a QA engineer knows software architecture and understands code that powers all those features that require testing. In this case, a QA specialist can use code as an additional source of information during testing. The underlying logic helps a QA specialist to track the related cases. White box tests are run mostly by developers.

What Is Gray Box Testing?

Gray box testing is a combination of the methods described above, so it implies partial knowledge of the product code. A QA specialist has limited access to the details about architecture and code. All the unique aspects remain a developers’ secret. Still, even limited access can be helpful when looking for context-specific errors.

Differences Between Black Box And White Box Testing

The fundamental difference between the two types of testing is clear, but let’s look into the details and compare black box and white box testing.

The black box testing suits perfectly for large code elements. Test cases are usually very detailed and specific about entry conditions, test steps, planned results, and test data. As for the white box testing, it is an effective solution that gives a technical opportunity to find and fix code lines with defects. Test cases focus on technical details and code particularities.

Black Box Testing Examples

During the black box testing, a QA engineer checks different inputs and outputs to make sure they match. Explained simply, a user can register in a system only if they enter a valid username and password. Therefore, a QA specialist needs to learn what ‘valid’ is for the product. After that, it is necessary to check how the system responds to both valid and invalid inputs.

For example:

• A user can register in the application if they enter a phone number in a required format or an email address without obvious mistakes (like @ missing) and a password that has at least one capital letter, one digit, and one symbol.
• If at least one of the requirements isn’t met, a corresponding error message appears on the screen, signaling that there is a mistake.
• An error message should be clear (verbal explanation instead of numerical error code) and highlighted (appear in a different color to attract attention).

It is essential to check the scenarios where a system can break. This is how we learn whether the software product responds to failing scenarios as expected. Invalid inputs can cause just inconveniences (an error message doesn’t appear on the screen) or cause app crashes.

For all these scenarios, a QA engineer doesn’t need to address software architecture or look into the code. They can see if the features work as expected without it. Thus, the backend stays locked in a box while we run tests on the surface.

White Box Testing Examples

During white box testing, you look into software code to check its logic. The coverage can differ – testing can cover separate statements, branches, or complete paths. As code syntax varies depending on a programming language, let’s take a look at the graphic representation of a registration path.

By inspecting a piece of code executing this path, a specialist can check the scenario of successful registration. However, it is not sufficient. What if a user has already registered in the system long ago and forgot about it? What if the password doesn’t meet the security criteria?

It is crucial to cover different scenarios on the backend – to have a piece of code for each. Otherwise, if a user cannot proceed with the registration, instead of tips and directions there will be silence. Therefore, it is necessary to test more complicated code snippets with decision statements and loop statements.

To Sum Up: Which One to Perform?

You cannot substitute white box testing for black box testing or vice versa. Both are essential for achieving the goal of the software testing process. Both have a specific purpose and place in the software development pipeline.

Used in combination, white box and black box testing enhance the QA check. They help to achieve maximum bug elimination, detecting defects through both interaction with software and discovering the root causes of those defects.