What Is Black Box Testing?

Software developers, quality assurance (QA) analysts, and testers use black box testing to ensure that code effectively meets user expectations. Black box testing techniques are used to identify security issues, usability issues, and evaluate external behavior. If you work on a software development team or are interested in testing your own programs, use the following article to learn more about different types of black box testing and how you can perform it yourself.

Read more: How to Write Test Cases: A Step-by-Step QA Guide

What is black box testing?

Black box testing, or closed-box testing, is a software testing technique that ensures your programs function as intended without requiring knowledge of internal code. These types of tests allow members of the team without technical knowledge or even end users to participate.

Black box vs. white box testing

Black box testing is a functional testing technique focusing on external behavior only, meaning you don't need access to the source code. In contrast, white box tests also take internal implementation into account. The white box software testing method can only be applied by those who understand the system's inner workings, which means it's typically carried out by developers or testing teams who have access to the source code.

How is black box testing performed?

First, you will want to determine the system requirements, such as the intended functionality or output signals that indicate the software is functioning correctly. Next, evaluate your inputs and test scenarios before generating test cases. It’s helpful to design test cases that test a wide range of input ranges. After this, you'll get outputs from these test cases and check whether they were successful by comparing the results with the expected output.

If your test cases yielded an unsuccessful result, you may need to fix the software or send it to the development team to repair the defects. After making corrections, you can rerun the black box testing process and reevaluate the outcome. Depending on your needs, you can choose different black box test cases such as decision tables, all-pairs tests, or error estimations.

Read more: How to Write Test Cases: A Step-by-Step QA Guide

Types of black box testing

Depending on your goal, you might perform black box testing in a few different ways. Black box testing plays a key role in software testing, ensuring that software applications meet their requirements and function as expected. The following covers a few types of testing you can choose from. 

1. Functional testing

Functional testing is one of the most common types of black box testing and involves tests to check the software system's functionality. To perform this type of testing, you might pick out specific functions, such as logging on to a site or checking out an item online. You might also check if certain functions have been integrated correctly or if the whole system functions together. A common example includes entering a PIN code to transfer money on an application. If the correct pin is entered, the transfer succeeds. If the incorrect pin is entered, the transfer fails.

2. Non-functional testing

Non-functional testing focuses outside of specific software functions. This involves things like the user experience, high user volume performance, security features, and compatibility across platforms. In these cases, you go beyond whether your program can perform the intended functions and how well it operates. 

3. System testing

System testing is performed on a program to ensure it runs effectively in different environments and situations. This testing ensures that customers or users will have an optimal experience regardless of where they run the program. This high-level test is performed after you validate the function of individual parts. 

4. Regression testing

Regression testing can help you ensure that code changes haven’t adversely affected the existing software functionalities. When you develop software, it's typically an iterative process. As you make changes and updates to your software application, new changes might disrupt previously working functionalities. This type of testing helps confirm that the old capabilities still work even as you integrate new functions. 

What are black box tests used for?

You can use this testing technique for several functions, depending on your type of software and user needs:

• Identify potential bugs and errors. A primary goal of black box testing is identifying any bugs, glitches, or errors in the application. By providing various inputs and observing outputs, you can detect discrepancies where the software doesn't behave as expected. This method helps eliminate unforeseen errors you might not see during the development phase.

• Verify specifications. Typically, you'll design a software application based on predefined specifications and requirements. Black box testing is a validation tool that ensures that the software functionality meets the initial requirements. 

• Assess user experience. Beyond functionality, you want your software application to give a positive experience for users. You can use non-functional black box testing to validate user experience, software reliability, and interoperability. This approach helps you gauge the software’s intuitiveness, flow, and user-friendliness.

• Evaluate security. You can also use black box testing to identify potential program vulnerabilities. You can use this type of security testing to inform whether you need additional security measures, such as firewalls or other cyber-attack prevention.

Pros and cons of black box testing techniques

When you test software, you'll want to choose the type of testing that most effectively meets your requirements. Like white box or gray box testing, black box testing has advantages and disadvantages. By knowing its strengths and limitations, you can decide whether it is the right kind for your needs.

Pros of black box tests

When deciding what type of software testing to use, you might choose black box testing for the following benefits. Some common pros include the following:

1. No need for internal knowledge 

One of the primary benefits of black box testing is that you don’t need in-depth knowledge of the internal structures or workings of the application. This means you can effectively conduct this test even if unfamiliar with the software.

2. Testing simplicity 

Because you often look for functionality with this method, this type of testing is simple to use on even highly intricate systems because you focus on inputs and outputs without much concern for the intermediary steps within the code.

3. Functional problem identification 

This testing method pinpoints issues concerning how the software executes actions. If your software isn’t performing as expected with a certain input, black box testing will likely catch it, given your test cases are comprehensive.

4. Unbiased error identification 

Software testers and developers are typically different people, meaning the code effectively gets “two sets of eyes.” This can help reduce any bias present during the code validation process.

5. Early error detection 

You can start black box testing as soon as the code has any level of functionality. This means you can start testing early and continue it as the code develops.

Limitations of black box tests

Depending on your needs, the drawbacks of black box testing may be something to consider. Commonly noticed disadvantages include:

1. Possibility of missing errors

Using black box testing requires some level of creativity to ensure you effectively test your code’s functionality. If you overlook a specific function, you may miss an error until after implementation. This inherently limits the ability of black box testing to test applications and systems.

2. Difficult to troubleshoot

If your code fails during black box testing, it might be difficult to understand exactly where it failed. Because you don’t know the internal structures, you might not know what part of the code caused the misstep. 

3. May require input specifications

Black box testing relies on input specifications. If you don’t know your inputs or the input type changes, you may be unable to build effective test cases.

How to start learning black box testing

Consider the following methods if you want to get started in black box testing:

• Pursue a certification. A degree in computer science or a related field can build a comprehensive understanding of software, algorithms, and other areas to enhance your testing capabilities. Some employers may certifications such as Certified Software Tester (CSTE) or International Software Testing Qualifications Board (ISTQB) Certified Tester.

• Get hands-on practice. By running practice tests as you learn, you can find areas of improvement and gain relevant experience. These practice sessions often present real-world challenges, allowing you to practice your testing skills in similar environments to what you would experience professionally.

• Explore online resources. You can find diverse online courses and sites that cover topics in software testing and other necessary fundamentals in this space. You can also find free YouTube tutorials or other online tools to help walk you through the basics of black box testing examples and more. 

Learn software testing with Coursera

Consider enrolling in the Foundations of Software Testing and Validation course by the University of Leeds on Coursera to learn about different testing techniques and their effectiveness. This beginner-friendly program covers topics like foundations of software testing and test design techniques.