When users open software solutions, they expect them to function as needed. For example, when a business analyst opens Excel, they hope to work with data without requiring knowledge of what’s happening with the application internally. If something breaks, they won’t be able to debug the software and fix what’s wrong. That’s why the black box model is so important.
Black box software testing evaluates application functionality without knowledge of the internal structures. This gives software engineers insight into how end-users view the app so they can adjust accordingly. The goal is to provide an application that meets end-user requirements and resists external attacks from bad actors. This article reviews black box testing examples and how a software development team can use it.
Common Types of Black Box Testing Approaches
Black box testing methodologies help development teams validate software applications by inputting data and observing what happens. That keeps projects on track to adhere to any functional requirements provided by business areas and locate defects related to software usability, performance, and functionality. Let’s look at common ways testers apply the black box approach to software testing.
Functional Testing
Functional testing focuses on ensuring that an application behaves as expected. For example, functional testing confirms precisely what happens if a user clicks a button on a retailer’s app to add an item to a cart. It’s also used to validate application inputs and outputs. An example is a tester attempting to enter text in a field that should only take numbers and then confirm that they receive a rejection prompt.
Non-Functional Testing
Testers use non-functional testing to assess whether a piece of software meets criteria critical to the user experience, like performance, scalability, and security. The main goal is to ensure that software applications perform as intended under specific conditions, like hefty traffic on a network. The non-functional testing process typically occurs after the completion of all functional tests.
Regression Testing
Developers often have to implement fixes for defects discovered during the testing process. Software changes can impact other functionality within the application. Regression testing helps ensure that recent software updates to one part of an application don’t affect the performance of different modules. It’s done without knowledge of a piece of software’s internal structures.
4 Black Box Testing Techniques to Try
Software teams and testers use several black-box testing techniques to validate systems against defined requirements and check for usability issues. Before we get into more details, let’s look at some of their most common methods.
- Requirements Review: Teams start by reviewing the application requirements provided by business stakeholders. The document should cover what users expect from the software and form the basis for developing test cases.
- Test Cases: Test cases cover specific inputs or conditions to evaluate a software application’s usability, functionality, and performance without prior knowledge. Examples of test cases teams might use include those that set boundaries for input ranges or verify that users can only log in when inputting valid credentials.
- Defect Recording and Reporting: Testers should document any issues found while testing, including the steps to reproduce the result, what was expected, and what occurred. Then, they should pass that information on to the development team for resolution.
1. Equivalence Partitioning: Grouped Test Cases
This black box testing technique divides input data into classes or partitions that exhibit similar behavior. Testers use equivalence partitioning to reduce the test cases required to thoroughly test a software application. This approach can be used to test various inputs, outputs, and values. For example, testers can set up partitions containing only invalid data that the software should reject.
If an input from one partition performs as expected, testers expect the other values it contains to pass. However, if a piece of data fails, other information in the class will likely also fail.
To perform equivalence partitioning, teams must determine all the possible inputs the software accepts. Then, they should use the software requirements to create classes of valid and invalid inputs. Finally, testers should pick one value from each equivalence class to test.
Below are examples of black box testing using equivalence partitioning.
Numeric Input: The tester wants to confirm that a numeric input field will only accept a user’s age between 1 and 100. So, they would set up two equivalence classes, one with numbers between 1 and 100 and another with ranges greater than 100 up to 200. The tester can then test any numbers from each class, like 32 and 108, to confirm whether the software application accepts and rejects each value as designed.
Text Input: The tester wants to confirm that a website’s text field will only accept usernames at least five characters long but no longer than 20. So, they’d create two sets of equivalence classes. The valid one would contain names within the defined ranges, while the other contained either too short (0-4 characters) or too long (greater than 20 characters).
2. Boundary Value Analysis: Edge Case Testing
Testers use boundary value analysis to locate and test input values near the edge of a software application’s input domain. The goal is to find any values likely to cause unexpected behavior that leads to errors because the program can’t handle them properly. This type of black box testing improves the software’s robustness and reliability.
Critical concepts of boundary value analysis include:
- Boundary Points: Values right at the edge of an equivalence partition, like 100 for a numeric input field that should only accept 1 to 100.
- Valid Boundary Points: Values within the acceptable range to be accepted into an input field.
- Invalid Boundary Points: Values that fall outside the acceptable range of values to be accepted into an input field.
An example of using boundary value analysis in black box testing is when testing a numeric input range. A tester would create boundary values and test cases that included data testing the upper (e.g., 99 (valid), 100 (valid), 101 (invalid)) and lower boundaries (e.g., (0 (invalid), 1 (valid) 2 (valid)).
The date input field is another example. If an input field should only accept dates for 2024, the tester would create boundary values below the lower boundary (e.g., 12/31/2023), at the lower boundary (01/01/2024), and after the lower boundary (e.g., 01/05/2024). They would also need to test the upper boundary with valid and invalid data (e.g., 12/24/2024, 12/31/2024, 01/01/2025).
3. Decision Table Testing: Logic Validation
This type of testing examines software behavior after testers enter various input combinations. It helps evaluate complex business logic applications and accept multiple input conditions. Decision tables help testers ensure they cover all possible input combinations for any production scenario.
The table, often called a cause-effect table, represents all potential inputs and corresponding outputs. Each table column contains unique combinations of input conditions, while each row contains rules or actions that result when those conditions occur. The place where a column and row intersect indicates if a condition is true or false and what action the tester should take.
Key decision table components include:
- Conditions: Inputs variables or conditions that affect the test outcome.
- Actions: Potential actions or outputs that can result from different combinations of conditions.
- Rules: Unique condition combinations and corresponding actions.
Software teams can create decision tables by listing the conditions that affect an outcome and the possible actions that can result. Determine the potential values or states for each condition (e.g., yes/no or true/false). Then, build rules by setting up different alternatives to cover all scenarios and define actions to take for every rule. Finally, organize all conditions, alternatives, rules, and actions into a table structure.
4. State Transition Testing: Dynamic Behavior Testing
This black box approach validates a system’s behavior as it moves between states while responding to various inputs or events. It’s most effective when testing an application where the state depends on the current input and historical values entered.
Critical components of state transition testing include:
- State: The situation that results from an object that allows it to satisfy a condition, perform an activity, or wait for an event.
- Transition: The movement from one state to another occurs when an application condition or event is triggered.
- Event: The action that causes a transition.
- Action: The operation that happens because of a state transition.
An application team might apply state transition testing with an ATM. A tester sets up tests to review transitions in an ATM under conditions like a user inserting their card, entering a correct or incorrect PIN, or performing a transaction. They may also create test cases to look at transitions when users perform functions like entering their User ID and password (valid and invalid data) or logging out of the system.
Optimal Uses of Black and White Box Testing
Both black box and white box testing, which include knowledge of an application’s internal code, are needed to achieve comprehensive software quality. Black-box testing focuses on the software’s external behavior, while white-box testing focuses on internal logic and code structure.
Black box testing is best used when testers want to:
- Validate requirements
- Ensure that user acceptance testing (UAT) goes over all the needs of users
- Test the integration of new modules into existing software to ensure they work together without issue
White box testing is best for situations where testers want to:
- Conduct unit testing to ensure different components work correctly under different conditions
- Test how data flows between different modules
- Perform code coverage analysis to ensure testing of all code sections
Software Testers Worldwide Trust Our Black Box Testing Tools
Ranorex Studio provides testers with everything needed to perform comprehensive software testing. Request a free trial to see what a difference our platform can make.
