What Is Black Box Testing, and Why Is it So Useful?

Sep 25, 2023 | Best Practices, Test Automation Insights

Black Box Testing

Black box testing is a common testing method that allows you to look at a software tool with a fresh perspective and see it how a user would. Using black box testing effectively will help your team maintain testing efficiency, utilize more of your staff, and keep your information confidential.

What Is Black Box Testing?

When someone tests a piece of software without knowing about the contents of the source code, they’re black box testing. The tester may know what a valid and invalid input should be, and they may know what a valid output should look like, but they’re able to ignore everything else.

Black box testing looks at the response time, reliability, and usability of the software tool. It is a popular choice for developers because it is easily scalable and reproducible, and it takes less time than more in-depth approaches such as white box testing.

By its nature, black box testing, which is also known as behavioral testing, must be completed by someone who is not on the development team. Because of that, it is occasionally completed by third–party developers, and it is especially useful for protecting confidential and proprietary information since the tester won’t be allowed to see the code.

Black box testing is ideal for identifying usability issues and problems with the interface. The tests are usually simple, and since the tester will only look at the test input data and results, they can be performed by a tester without a lot of coding experience. This is especially true if the testing is done using Gherkin language or record-and-replay software, which is designed to allow developers without coding experience to still build effective tests.

Black Box vs. White Box Testing

While black box testing can tell you whether a function was completed and if it was successful, it can’t show you how or why a particular test failed. It’s also difficult for the tester to verify that each individual part of the software tool has been tested, since they don’t know what each of its component parts are.

That’s where white box testing comes in. Unlike its counterpart, white box testing involves a full understanding of the source code being tested. It is usually performed by members of the internal team for static code analysis, mutation testing, and integration testing. It not only allows the tester to see whether an input gave the right output, but it also allows them to look at the internal architecture and configuration of the source code to understand why it gave that outcome. This can enable testers to pinpoint specific issues with the code and mark them for improvements.

White box testing is popular for checking software integrations and running a continuous integration and continuous deployment (CI/CD) pipeline. However, white box testing does require the developer to have experience with coding, and ideally that specific source code, to be effective.

What Is Gray Box Testing?

As the same implies, gray box testing is somewhere in between black box and white box testing. It means that the tester has partial knowledge of the source code, but not all of it. It is often used in security testing, since the hacker may have partial knowledge of a system’s code, but not necessarily all of it. Gray box testing does require a division between the developers who may know too much about the source code and the testers who need to have limited knowledge for it to be a successful gray box test.

Types of Black Box Testing

Functional Testing: This is the most basic form of black box test, it simply verifies that the software tool is functional. It verifies that when you put in a value, you get a value in return.

Non-Functional Testing: This category of test seeks to determine how well a tool works. It asks: How well does it perform? Is it reliable? And is the interface usable?

Regression Testing: These are completed after the code has been updated to make sure that the tool is still working properly, and no new issues were introduced.

Black Box Testing Techniques

In order to ensure solid test coverage while preventing redundant tests and getting bogged down in inefficiencies, an effective tester will need to choose the right black box testing technique. There are many different types of tests available, and we’re going to go over some of the most popular.

Equivalence Partitioning

This type of testing is done when there are specific sets of inputs that would have specific sets of expected outcomes. Let’s say you’re testing a tool for entering quiz scores that work by a pass/fail grade. You can choose 0–60 as one partition (failure) and 61–100 as the other (passing). Then choose a value from each to represent that partition in your test, such as 30 and 80. Presumably, all the other values within each partition should produce the same result.

Boundary Value Analysis

Boundary value analysis assumes that the values that are most likely to have issues are the ones at the boundaries of your partition. It takes a value from each end of the partition for testing. Using the quiz score example from above, you would likely choose 0, 59, 61, and 100 as your boundary values for testing.

Edge Case Testing

Unfortunately, not all of your users will enter inputs that are expected, and some may (intentionally or otherwise) enter extreme inputs. Edge case testing verifies that these types of inputs won’t break the tool and will give the user an output that might help direct them toward a more actionable input.


This method is best done by experienced testers since it involves guessing which inputs would be the most likely to produce errors. After developers have performed tests, especially continuous tests of specific software, they can develop an instinct for which inputs would be representative. Obviously, the biggest challenge with this approach is that it is arbitrary and could run into endless tests if not reigned in.

Ranorex Black Box Testing Tools

Black box testing tools are effective, but they can also be tedious and time-consuming to implement. Save your staff valuable time by using automated testing software from Ranorex. Our software has a suite of powerful tools that are designed to help developers implement a wide range of tests across desktops, mobile devices, and web browsers—including both real-world devices and emulators.

Start a Free Trial of Ranorex

Ready to start using black box testing to ensure a great experience for your users? Start a free trial of Ranorex today to build effective automated tests that will save your team time and money.

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