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11 March 2024

11 Min. Read

Black Box Testing

What is Black Box Testing- Techniques And Examples

What is Black Box Testing- Techniques & Examples

Key Highlights

In this blog, we cover the following highlights:

  1. Learn about the concept of black box testing

  2. Get to know the types of this behavioral testing approach

  3. Know about the modern tools that helps in testing solely the input and output of a software

  4. Lastly, learn how to perform the various types of black box testing

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Black box testing is a technique where testers evaluate the functionality of the software application without looking into its internal structure or workings. This method treats the software as a “black box”— the tester knows nothing about what goes on inside the box and focuses solely on the input that goes into the software and the output that comes out of it.


The main goal is to test how the software behaves and responds to various inputs, and how it performs under different conditions. This approach is based entirely on the software requirements and specifications.


What is Black Box Testing?

Black box testing is a comprehensive software testing method that evaluates a software application’s functionality without requiring knowledge of its internal workings, focusing instead on its input and output. This method, also known as behavioral testing, is crucial for ensuring that software behaves as expected under various conditions, without the need to understand its internal code structure, implementation details, or internal paths.


Techniques of Black Box Testing

Several techniques are employed in Black Box Testing to ensure comprehensive coverage of the software's functionality:


1.Equivalence Partitioning: This technique divides input data of the software into partitions of equivalent data from which test cases can be derived. The rationale is that if a single condition in a partition works, then all other conditions should work as well.


Equivalence Partitioning divides input data into partitions of equivalent data. The assumption is that if one condition in a partition passes the test, the other conditions in the same partition should also pass.


Example: Consider a login feature that accepts a password length of 6 to 12 characters. You can divide the input data into three partitions:


  • Less than 6 characters (invalid)

  • 6 to 12 characters (valid)

  • More than 12 characters (invalid)


# Pseudocode for equivalence partitioning test
def test_password_length(password):
    if len(password) < 6 or len(password) > 12:
        return False
    else:
        return True

# Test cases
assert test_password_length("12345") == False  # Test with less than 6 characters
assert test_password_length("123456") == True  # Test with 6 characters
assert test_password_length("123456789012") == True  # Test with 12 characters
assert test_password_length("1234567890123") == False  # Test with more than 12 characters

2. Boundary Value Analysis: This focuses on the values at the edges of equivalence partitions. It is based on the theory that errors are more frequent at the boundaries of input ranges.


Boundary Value Analysis focuses on the values at the edges of input ranges, where most of the errors occur.


Example: Using the same login feature, you would test with passwords of lengths 5, 6, 12, and 13 characters to focus on the boundary values.


# Test cases for boundary value analysis
assert test_password_length("12345") == False  # Boundary value just below valid range
assert test_password_length("123456") == True  # Boundary value at the lower end of valid range
assert test_password_length("123456789012") == True  # Boundary value at the upper end of valid range
assert test_password_length("1234567890123") == False  # Boundary value just above valid range

3. Decision Table Testing: This is used for functions that have logical relationships between inputs. A decision table represents different input combinations and the corresponding system behavior.


It is used when the system's behavior is determined by a combination of inputs. It's particularly useful in scenarios where different input combinations result in different actions.


Example: A simple discount calculation system where the discount depends on the type of customer ("Regular" or "Premium") and the purchase amount.

Customer Type

Purchase Amount

Discount

Regular

< $100

0%

Regular

>= $100

5%

Premium

< $100

10%

Premium

>= $100

20%


def calculate_discount(customer_type, purchase_amount):
    if customer_type == "Regular":
        if purchase_amount >= 100:
            return 5
        else:
            return 0
    elif customer_type == "Premium":
        if purchase_amount >= 100:
            return 20
        else:
            return 10

# Test cases
assert calculate_discount("Regular", 50) == 0
assert calculate_discount("Regular", 150) == 5
assert calculate_discount("Premium", 50) == 10
assert calculate_discount("Premium", 150) == 20

4. State Transition Testing: This technique is useful where the system transitions from one state to another based on inputs. It helps in identifying valid and invalid state transitions.


def add(a, b):
    return a + b

# Test cases
assert add(2, 3) == 5
assert add(-1, -1) == -2
assert add(-1, 2) == 1

5. Regression Testing: Regression Testing ensures that new code changes do not adversely affect existing functionalities. It's critical after bug fixes, enhancements, or any code modifications.


Example: After adding a new "subtract" function to the calculator, ensure the "add" function still works as expected.


# Assuming the add function is as defined earlier

def subtract(a, b):
    return a - b

# Regression test cases for the add function
assert add(2, 3) == 5
assert add(-1, 1) == 0

#

New test cases for the subtract function:
```python
assert subtract(5, 3) == 2
assert subtract(-1, -1) == 0

Case Study: The iOS 8 Update Rollout

Apple released iOS 8 with much anticipation, introducing a range of new features and improvements over its predecessor. However, soon after its release, users began reporting significant issues.


Regression Error: The problem was linked to a regression error in the software update. Specifically, the HealthKit feature, which was supposed to be a major new addition allowing health and fitness apps to communicate more effectively, was found to be buggy and was pulled from the App Store just before the iOS 8 launch.


Consequences:

  • User Impact: The regression error not only delayed the launch of HealthKit-compatible apps but also affected the overall user experience negatively. Users who had updated to iOS 8 found themselves facing various issues, including problems with connectivity, battery life, and third-party keyboard support.


  • Reputation Damage: Apple's reputation for releasing polished and thoroughly tested software was tarnished. The company had to work quickly to address these issues, leading to the release of iOS 8.0.1.


  • Further Issues: Unfortunately, the iOS 8.0.1 update intended to fix these problems introduced new issues, most notably disabling cellular service and Touch ID for a number of users. This forced Apple to pull the update and release iOS 8.0.2 shortly after.


Lessons Learned

This example serves as a cautionary tale about the importance of comprehensive testing and quality assurance in software development. Despite Apple's extensive resources and experience, a regression error slipped through, affecting millions of users worldwide. It underscores the critical need for robust regression testing frameworks to catch such errors before they impact end-users, especially in major software releases.


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Types of Black Box Testing

Black Box Testing can be categorized into several types, each focusing on different aspects of the software:


  • Functional Testing: Tests the functionalities of the software against the specified requirements.


  • Non-Functional Testing: Focuses on aspects that are not related to specific behaviors or functions of the software, such as performance, usability, and scalability.


  • Regression Testing: Conducted after changes (like fixes or enhancements) have been made to the software, to ensure that the changes haven't adversely affected existing functionalities.


Process of Black Box Testing

The process of conducting Black Box Testing involves several systematic steps:

  1. Understanding Requirements: The first step involves thoroughly understanding the software's requirements and specifications.

  2. Selecting Inputs: Based on the understanding of the requirements, testers select inputs to test how the software behaves with them. Both valid and invalid inputs are chosen to see if the software correctly processes them or properly handles errors.

  3. Determining Expected Outputs: For each input, the expected output is determined based on the software's specifications.

  4. Executing Test Cases: Testers then execute test cases with the selected inputs and record the software's output.

  5. Comparing Outputs: The actual outputs are compared against the expected outputs to check for discrepancies.

  6. Reporting and Fixing: Any deviations from the expected outputs are reported as defects. These are then fixed by the developers, after which the tests are re-executed to confirm the fixes.


Tools for Black Box Testing

A variety of tools can be used for Black Box Testing, depending on the specific requirements of the testing process. For functional and regression tests, tools like QuickTest Professional (QTP) and Selenium are popular choices. For non-functional testing aspects such as load and performance, tools like LoadRunner and JMeter are widely used.


1. Selenium - Tool for Black Box Testing

Selenium is an open-source tool used for automating web browsers. It allows testers to write scripts in various programming languages like Java, Python, C#, and Ruby, enabling automated interaction with web pages. This tool is especially useful for testing web applications, ensuring they work across different browsers and platforms.


Example: Consider testing a web-based email client. Selenium can automate tasks like sending emails, attaching files, or deleting emails, ensuring these functionalities work seamlessly across various web browsers without the tester manually performing these tasks in each browser.


2. QTP/UFT (Unified Functional Testing) - Tool for Black Box Testing

2. QTP/UFT (Unified Functional Testing) - Tool for Black Box Testing

QTP/UFT is a commercial tool from Micro Focus that provides functional and regression test automation for software applications and environments. UFT supports keyword and scripting interfaces and integrates with other Micro Focus tools like Quality Center for comprehensive test management.


Example: In testing a retail banking application, UFT can automate scenarios like account creation, fund transfers, or loan application processes, simulating the actions of a user to verify that the application behaves as expected under different scenarios.


JMeter - Tool for Black Box Testing

3. JMeter - Tool for Black Box Testing

JMeter is an open-source tool designed for load testing and measuring the performance of various services, with a focus on web applications. It can simulate a heavy load on a server, network, or object to test its strength or analyze overall performance under different load types.


Example: For an e-commerce website, JMeter can simulate thousands of users

accessing the site simultaneously to browse products, add items to the cart, and checkout, helping to identify bottlenecks or performance issues under high traffic conditions.


Appium - Tool for Black Box Testing

4. Appium - Tool for Black Box Testing

Appium is an open-source tool for automating mobile applications. It supports both iOS and Android platforms, allowing testing of native, hybrid, and mobile web apps. Appium utilizes the WebDriver protocol to interact with mobile applications as a user would.


Example: Testing a food delivery app, Appium can automate tasks such as searching for restaurants, adding food items to the cart, and completing an order. This ensures the app's functionality across different devices and operating systems.


5. Postman - Tool for Black Box Testing

5. Postman - Tool for Black Box Testing

Postman is a popular tool for API testing, allowing users to send HTTP requests to test RESTful APIs and SOAP Web services. It provides a user-friendly interface for constructing requests, reading responses, and automating tests through scripting.


Example: For a social media application, Postman can test APIs responsible for user authentication, posting updates, and fetching user feeds. By automating these API calls, testers can quickly verify the backend functionality supporting the application's front end.


Importance in the SDLC

Black Box Testing plays a vital role in the Software Development Life Cycle (SDLC). It ensures that software meets the functional and non-functional requirements specified by the stakeholders, thus guaranteeing quality and reliability.

Black Box Testing is relevant at various stages of the SDLC, from the initial requirements phase to the final testing phase before release.

Challenges

While Black Box Testing is crucial for validating software functionality, it has its challenges and limitations. Testers may not have complete coverage of the application if the specifications are not detailed enough.


Additionally, without knowledge of the internal structures, it may be difficult to identify certain types of defects.


Conclusion

Black Box Testing encompasses a variety of techniques and types, each designed to validate different aspects of software functionality and performance. Through examples like equivalence partitioning, boundary value analysis, decision table testing, and specific types of testing such as functional and regression testing, we can see how Black Box Testing applies in practical scenarios. The hypothetical code blocks provide a glimpse into how these tests could be structured in a real testing environment.


The essence of Black Box Testing lies in its ability to assess software from the user's perspective, ensuring that the application meets its requirements and behaves as expected under various conditions. By focusing on inputs and outputs, Black Box Testing simplifies the testing process, making it accessible even to those without detailed knowledge of the software's internal workings. Whether testing a simple calculator app or a complex web application, the principles of Black Box Testing remain the same, emphasizing functionality, usability, and overall user satisfaction.


By integrating Black Box Testing into the development lifecycle, teams can identify and address potential issues early, improving the quality and reliability of the final product. This approach not only enhances the user experience but also contributes to the software's long-term success in a competitive market.

Frequently Asked Questions (FAQs)

1. What is meant by black box testing?

Black box testing is a method where the internal workings of a system are not known to the tester. It focuses on input and output without considering the internal code structure.

2. What is an example of a black box?

A website search engine is an example of a black box. Users input queries, and the engine provides results without revealing its internal algorithms.

3. Why is black box used?

Black box testing is used to assess software functionality, identify errors, and ensure that the system behaves as expected without knowledge of its internal code, promoting unbiased testing.
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