What is Black Box Testing?

Black box testing is performed without any knowledge of the internal workings of the system. This independence from the code allows testers to focus on the software’s functionality rather than its internal structure.

Black box testing can uncover hidden errors and discrepancies that may not be apparent during white box or unit testing. It ensures that the software behaves as expected when it interacts with users and other systems. Let’s learn more.

Black box testing is a software testing methodology where you evaluate software features/functions without understanding the internal code structure or how the code works behind the scenes.

Simply put, you provide input or perform an action and see if the output is right or if the feature works as expected as per project specs/requirements.

For instance, when you fill out a message form on a website, you see it gets submitted without errors. You are not concerned with how that form is connected with the servers or how its code has been written. In black box testing, you just confirm that the form submission is successful without issues.

Some prominent black box testing tools include:

• Selenium
• Playwright
• Cypress
• WebdriverIO
• Katalon Studio

Here’s how black box testing improves the working quality of your software:

Validates the Proper Functioning of Your Software

Black box testing confirms that your software is functioning as expected and delivers the right output. It’s especially beneficial for larger systems where you have a large number of features. With black box testing, you ensure that nothing breaks function-wise.

Reflects User Experience and Real-World Software Usage

Software usage can be unpredictable, varying greatly among users. Black box testing ensures that your software’s features, user experience, and functionality are free from issues, providing a seamless experience for the end user. The intricate workings of your software remain hidden from users, who simply expect it to perform as intended. Black box testing validates this expectation, confirming that the software operates as desired.

You Don’t Need to Understand Code

When you conduct black box testing, you don’t have to worry about how functionalities or workflows are implemented in the software source code. All you need to test is that when you provide the correct input or perform an action, you get the expected output or result. It’s just like you drive a car without knowing how the engine works.

Lowers Chances of False Positives

The results of black box testing have lower chances of being flagged as false positives. This implies that if a function is malfunctioning, black box testing typically makes it evident. The probability of erroneously deeming a function as operating correctly when it produces incorrect results or exhibits unexpected behaviors is minimal.

Enhances Test Coverage

Black box testing significantly broadens your software testing scope and therefore enhances your test coverage. It benchmarks your software from an end-user perspective with a variety of inputs and user interactions, and in the process, uncovers any defects or bugs resulting in comprehensive testing of your software.

Validates Functionality Without Compromising Proprietary Code

Black box testing does not necessitate knowledge of the internal code structure, thereby protecting your source code from potential tampering during validation with third-party applications or when outsourced to external testers who may not be part of your core team.

Also Read: STLC: Getting Started with Software Testing

With black box testing, you need to prioritize what to test in your software. Here’s a list you can borrow:

Correct Results

Black box testing involves verifying if the output aligns with the expected results given specific inputs for different functionalities.

Usability & UI/UX

Black box testing allows you to assess your software for optimal usability. Your goal is a streamlined, user-friendly interface with minimal distractions.

Error and Exceptions Handling

Black box testing verifies that users are not caught unawares by invalid inputs, thanks to well-managed software errors. Instead, all error-handling workflows in your software provide clear messages or outputs, indicating the nature of the problem and the necessary corrective actions.

Boundary Values

Black box testing also verifies the boundary values for different functionalities in your software. It’s crucial to test and validate edge cases or extreme scenarios in your software. This form of testing can reveal issues or bugs associated with boundary conditions.

Software Interoperability

Modern systems are often developed with various other sub-systems, layers, and components. With black box testing, you can ensure that your software interacts and functions as expected with all integrations or subsystems.

Also Read: Unit Testing vs. Integration Testing

Software Compatibility

Black box testing helps ensure that your software is platform-agnostic and runs and functions as expected across different platforms. It helps you identify any issues or defects in your software functionalities when you run it across different browsers, systems, and devices.

Software Performance

Black box testing is really handy while benchmarking your software performance, response times, latencies, lags, and so on. You get insights into how well your software performs from an end-user perspective and if there are any issues with it to have them fixed.

Software Security

Black box testing can also reveal loopholes in your software or ambiguous behavior in your authentication and authorization functions. Since black box testing tries to reflect real-world scenarios without concerning internal code workings, security issues, if any, that are user-facing can be identified, reported, and fixed promptly..

Black box testing is broadly classified into three types. Let’s briefly cover each type:

Functional Testing

Functional testing focuses on examining your software’s functional aspects. It validates that specific functions operate correctly and meets the established criteria or software specifications.

Read More: Functional Testing: What to Test, Why to Test, Types, and More.

Non-functional Testing

Non-functional testing in black box testing helps validate the non-functional attributes of your software. You test for your software performance, security, user experience, and usability with black box testing techniques.

Regression Testing

With regression testing, you ensure that the recent code changes or fixes have not affected your existing system functionalities. You also ensure that new and unexpected errors are not introduced in your system as a result of those code fixes.

Let’s quickly cover the top black box testing techniques for software testing:

Equivalence Class Testing

The equivalence class testing method partitions the input test data into congruent classes or groups. The output is then evaluated for each of these groups. This approach is designed to reduce the quantity of test classes while enhancing test coverage effectively.

For instance, you test the login form with two sets of credentials. One valid (first equivalence class) and one invalid (second equivalence class) and check for the results.

Another example can be the case of age validation to avail of an insurance scheme of an XYZ company. You check for results with three equivalence classes. First for ages below 18 years, second for ages between 18 - 65 years, and third for ages above 65 years.

Boundary Value Testing

Boundary value testing involves examining values at the edges of the defined input range or valid extremes, aiming to identify issues related to boundary conditions.

For example, consider a registration form with a birth year field that accepts inputs from 1980 to 2000. Rather than testing all possible values, you would verify the system’s responses or behaviors for the birth years 1979, 1980, 2000, and 2001, which are at or near the boundaries of the accepted range.

Decision Table Testing

The decision table testing method involves creating a decision table that maps various combinations of inputs to their respective decisions or outputs produced by your software. This technique allows you to compute all potential outcomes based on these input combinations.

For example, suppose you’re validating the discounts provided to different types of customers. In this case, you would create a decision table where the columns represent different purchase ranges, and the rows represent varying discount percentages based on the customers’ historical purchasing amounts.

State Transition Testing

The state transition testing method involves verifying the behavior of a system or function based on its current state. The goal is to test and confirm whether the functions operate as outlined in the software specifications.

For example, consider an e-commerce application where you’re validating the payment functionalities in two distinct states: logged in and logged out. You would ensure that a user can make purchases and that payment processing is permitted exclusively when the user is in the logged-in state.