What is Black Box Testing: Techniques, and Best Practices

OVERVIEW

Black box testing is a software testing methodology that focuses on the functional requirements of a system without considering its internal workings or implementation details. The tester need not have any knowledge of the internal structure or design of the system.

It ensures that a system meets the requirements specified by the customer or user. A black box test can be conducted at different levels, including unit testing, integration testing, and system testing. In order to identify defects and ensure that a system works properly, running black box tests is a valuable approach.

Black box testing is a software testing method that examines the software without prior knowledge of its internal structure. It can be contrasted with White box testing, which involves a more in-depth knowledge of the software's implementation details.

In theory, Black box tests can be run by anyone, independent of the development team, and a developer's familiarity with the code should not affect how well their code is tested; conversely, White box tests tend to require a developer's intimate understanding of the code to construct test cases.

So the primary job of a software tester while running Black box tests is to test the functionalities of software applications when the internal paths & code structure are not known.

The customer's set of detailed requirements for the product is tested. These requirements are related to different functions, so a tester chooses a function, enters an input value, and examines the output. If the function's result is correct, it is passed in testing.

It is also sometimes referred to as behavioral testing, as instead of the technical perspective, behaviors are considered from the point of view of a software program in various situations.

The need is to determine how a software program behaves instead of focusing on the technical aspects under various conditions. It also helps you to identify different errors like:

• Performance errors.
• Usability errors.
• Functionality errors.
• Initializing & terminating errors.
• Concurrency & timing problems.
• Bridge the communication gap.

In this section, we will discuss some of the benefits of executing Black box tests.

• The way users interact with a product and their overall perception, i.e., tests are performed from the user’s point of view. Things like meeting customers’ expectations & discrepancies in the specifications are tested.
• Developers and testers work independently to avoid bias.
• Big and complex software systems can be tested more effectively using this method. It is especially useful for the testing of large systems.
• Testers do not need technical knowledge or programming skills. They do not need to know IT jargon or how the software has been built.
• Little chance of false positives.
• If a defect is detected early in the testing process, you can correct it easily.

By definition, Black box tests are done without seeing the inner workings of the application. That said, there are still limitations to what you can accomplish with this method.

• Only a limited number of inputs can be tested, and many program paths will not be checked.
• In many projects, there are no clear specifications. This can make test case design challenging.
• If you don't have technical or programming experience, the risk is that you might not consider all the possible circumstances in your scenario.
• Complete test coverage is impossible.
• It is possible to accelerate the testing process by skipping testing inputs and outputs that are not currently being used.
• If a software designer/developer has already run a test case, additional tests may not be necessary.

Black box tests ensures to keep a check on the input that enters the software while checking the desired output. Below is the scope of Black box tests.

• Test your software easily so that desired use is fulfilled.
• Testers can perform this operation without any coding knowledge of the application.
• It helps examine the functionality of the software.

Black box testing is used in three main types of software testing: functional, non-functional, and regression.

• Functional Testing

We test the functionality of a software program by specific functions or features of the software. The functional requirements of a system are tested, for example, logging in to an eCommerce site through the correct credentials & also checking through the wrong credentials whether the desired output is obtained.

• Non-functional Testing

In non-functional testing, there is a focus on “HOW’. It doesn’t test if the features & functions are performed well but focuses on the how part of testing. Non-functional testing is never carried out before functional testing.

• Regression Testing

After a fix, upgrade, or other system maintenance, regression testing is done to ensure the new code hasn't adversely affected existing code. It is used to determine whether a new version of the software performs as well as or better than the previous version. It's possible that a fixed defect could have introduced another defect.

Many different Black box test techniques help in testing various features of the software. There are several techniques available out there, but not all of them can be used for every type of application. Some basic techniques are:

• Equivalence Partitioning

In this, we need to break up possible inputs into groups and test one example input from each group. An equivalence class is a set of data items considered equivalent to each other, so it will receive the same processing when sent as input to an application.

For example, a food company's software might charge different subscription fees for people who are already members for 2 years & different for new members. In this case, it is sufficient for testers to check only one case from each group.

• Boundary Value Analysis

This technique is closely associated with equivalence class partitioning. A system exhibits a special response at a specific value of an input; that specific response at that specific value is called its boundary. We analyze the application's behavior with test data at the boundaries of equivalence classes.

For example, a specific field may accept only values within that range, like supposing a range is 0 to 100. The tester will see if the system accepts and rejects inputs correctly when the number above is entered.

• Decision Tables

Testing the application’s behavior based on different combinations of input values is called decision tables testing. Many systems provide outputs depending on the conditions in which they are operating. The columns each have a unique combination of elements. Testers can identify the conditions that must be satisfied for a rule to apply, determine the outcome of each rule, and design a test case for each rule. The functions that have a logical relationship between two or more inputs are appropriate.

• State Transition Testing

It is a way to determine what the software application does when different values of input are given to the same function. Generally used in cases where there is a transition from one state to another. Like in the case of the login mechanism where after a specific number of failed login attempts, it goes into a transition where the locking of the account takes place.The testers here design test cases that probe the system when it transitions states.

• Error Guessing

This technique involves identifying common errors developers make when building similar systems. It’s a way to identify errors without setting forth a specific method. The tester will be guided by experience when trying to find unknown problems in software here.

• Use Case Testing

Use case testing is a form of software testing that uses use cases. As per the usage of the system, they are used to identify the test cases from start to end. A test scenario is created based on the functionality of each function from beginning to end.

• Cause-Effect Technique

It's a technique that explains the relationship between a result and all the factors that impact it. Dynamic test cases are used here. This technique, also called the cause-effect graph technique, is based on a collection of requirements and is used to determine the minimum number of tests that can cover the maximum number of sections in the software.

The cause-and-effect graph technique can convert the requirements specification into a logical relationship between input and output conditions.

• All Pair testing Technique

It is also known as pairwise testing. It is used to test all the possible combinations of values. The applications that use checkbox input, radio button input, list box, and text box use this combinatorial method.

With so many options to choose from, it can be hard to find the right tools you need to test applications. Here are some of the most common tools

• Selenium - Selenium is a browser automation tool that lets you write scripts in the programming language of your choice. Selenium provides a variety of drivers to support almost all web browsers., and it lets you perform different actions in each browser.
• Appium - Appium is a community-driven open source project that's developing an open standard for automated testing of mobile websites and apps. It is a cross-platform testing framework, supporting both Android and iOS native apps and websites accessed through mobile browsers.
• LoadRunner - LoadRunner, from Micro Focus, is a testing tool that measures how applications behave under heavy loads. LoadRunner helps you test mobile apps by measuring their performance, scalability, and capacity.
• JMeter - JMeter is a Java-based load and performance testing tool that works with JDK 5 or higher. It's used to test the performance of Web applications and other types of software under heavy loads.

In this section, let's look at how to run your Black box tests.

• Determine and understand the software application's requirements and specifications.
• Check valid and invalid inputs along with expected outputs to validate that the system identifies them appropriately.
• Create automated test cases with multiple test scenarios and inputs.
• Run the test cases.
• Validate the desired results with the actual results.
• Resolve test case errors.
• After, re-test the application to avoid recurring bugs.

While performing testing, you must also take different browsers, browser versions, devices and operating system into account. It ensure your software applications works perfectly across each configuration.

Instead of procuring every browsers, devices and OS for your target audience, consider using a cloud-based testing infrastructure like LambdaTest.

LambdaTest's real device cloud offers 3000+ real browsers, devices and OS for manual and automation testing. Therefore, you can check how your website or app renders and works on different browsers, devices, and OSes. With LambdaTest test automation cloud, you get faster test execution speeds and faster developer feedback. This in turn cuts down overall costs related with finding issues at later stages of software development.

With LambdaTest Automation testing platform, you can automate web testing with various automated testing tools like Selenium, Cypress, Playwright, Puppeteer, TestCafe, Appium, Espresso, etc.

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An example of black box testing is evaluating a web app's login feature without insight into its code. This involves checking if the login page works correctly with the correct user credentials.

Test Case Name: Validate Successful Login Using Correct Credentials

Test Procedure:

• Launch the web browser.
• Navigate to the login page by entering its URL.
• Input a correct username in the designated username input field.
• Input a correct password in the designated password input field.
• Select the “Login” button to submit the credentials.
• Await the system's response to the login request.

Expected Outcome: The system should grant access, redirecting the user to the main dashboard or homepage of the application.

Test Case Outcome: PASS (upon successful redirection to the dashboard/homepage)

Test Case Name: Validate Login Failure with Incorrect Credentials

Test Procedure:

• Launch the web browser.
• Navigate to the login page by entering its URL.
• Type an incorrect username (for instance, “usernotfound”) in the username input field.
• Type an incorrect password (for instance, “incorrectpass”) in the password input field.
• Select the “Login” button to submit the credentials.
• Await the system's response to the login attempt.

Expected Outcome: The system should deny access, displaying a specific error message (such as “Invalid username or password”) on the login screen to indicate the failure of the login attempt.

Test Case Outcome: PASS (if the specified error message is correctly displayed)

Let's look at the differences between Black box and White box testing.

In this guide, we have covered some of the main points regarding Black box testing, its advantages & disadvantages so you can decide in what situations you should do it.

Happy Testing!!!