Software Development Updates

Black Box vs White Box Testing involves two different approaches to software testing: Black box testing involves testing the software without knowledge of its internal workings, while white box testing requires the tester to understand the system’s internal structure and logic.

With this blog, we’ll understand Black Box testing and White Box testing approaches with their respective pros, cons, testing techniques, and scenarios for their use. This will help in choosing the right software testing services based on the project needs. We’ll discover the significant differentiating points between the testing methods.

1. What is Black Box Testing?

Black Box testing is a type of specification-based testing that focuses on the application from the perspective of end users, aligning with their expectations and business goals. QA professionals thoroughly evaluate the outputs against the provided input values to check the application’s functionality in various external scenarios. They perform a comparative assessment of the system’s actual working against its expected performance. You can also call it opaque box testing or closed box testing because it does not focus on the internal design and working of the application, similar to how users are not concerned with the internal code structure.

Black box testing is conducted after the software development process is complete. Software testers do not need extensive programming knowledge to create test cases and perform testing. They design test cases based on the input-output relationship, keeping user and business requirements in mind. A report dealing with the bugs detected during testing is then sent to the development team for resolution.

There are three types of Black box testing:

1. Functional Testing: It verifies that all the software’s functionalities operate according to the requirements and specifications.
2. Non-Functional Testing: It tests the software against non-functional aspects, for example, usability, performance, and scalability.
3. Regression Testing: It assesses the software’s functionality after modifications have been made to ensure that these changes do not negatively impact existing features.

1.1 Advantages of Black Box Testing

• User-Focused Testing: Black box testing simulates real-world user interaction with the software, providing valuable insights into user experience and enhancing customer satisfaction.
• Less Time-Consuming: Testing is faster because it does not require an examination of the system’s internal workings.
• Highly adaptable testing method: Black box testing can be applied to any type of application, regardless of its source code or complexity, as it focuses only on the user interface.
• Cost-effective: It can be performed by companies with budget restrictions, as testers do not require technical knowledge to understand the internal structure of the application.

1.2 Disadvantages of Black Box Testing

• Restricted Test Coverage: Testing only deals with the software’s visible parts, ignoring the possibility of structural bugs.
• Requirements Dependency: Testers evaluate the software based strictly on user requirements, which can be ambiguous or incomplete, resulting in unreliable testing outcomes.
• Redundancy: The trial and error method can lead to redundant test cases that concentrate on the same aspects of the software, wasting time and resources.

1.3 Techniques of Black Box Testing

The following are the Black box testing techniques that can be used according to the requirements.

• Equivalence Partitioning: As the name suggests, this technique categorizes the input data set into equivalent sets or partitions of valid and invalid inputs. This means that each input value within a partition will produce the same output. Therefore, it’s not necessary to test every input in a class. You only need to design a single test case for the equivalent partitions to ensure comprehensive test coverage.
• Boundary Value Analysis: This technique, also known as ‘Range Checking,’ assesses the range of input values by testing the upper and lower limits. There is a high possibility of errors at these extreme ends, so testing at these points becomes crucial.
• Decision Table Testing: This technique uses a decision or cause-effect table to test different combinations of inputs with their corresponding outputs. The row represents conditions, and the column represents actions.
• State Transition Testing: It evaluates the system behavior when transitioning from one state to another in response to varied input values.
• Error Guessing: This informal black box testing technique relies on the tester’s knowledge of the software’s requirements and their previous experience with similar software applications to identify defects in the system. It is carried out after formal testing.

2. What is White Box Testing?

White box testing is a detailed code-based testing method that examines the internal structure of the software. Test coverage includes branch coverage, analysis of source code, paths, modules, data structures, loops, and data flow. It is considered low-level testing as it focuses on verifying every aspect of the internal coding and design. Testers are technical experts with complete knowledge of the system architecture to design test cases accordingly. You can also refer to white box testing with names like “transparent testing”, “glass box testing”, “clear box testing”, and “open box testing”.

White box testing examines the internal code structure by breaking it into different constituent units. This type of structural testing is a comprehensive technique to uncover potential security vulnerabilities, identify broken or redundant conditional logic, and highlight gaps in software’s expected behavior.

The following are the prominent categories of white box testing:

1. Unit Testing: It tests the working of the isolated code blocks of the internal code structure.
2. Integration Testing: It evaluates the working of the combination of code blocks.
3. Mutation Testing: Mutations or modifications are introduced in the source code, and test cases are evaluated based on their ability to detect the changes.
4. Penetration Testing: The attacker has complete knowledge of the system to perform a targeted attack.

2.1 Advantages of White Box Testing

• Thorough Testing: White box testing ensures complete coverage of the internal code structure.
• Code Optimization: Line-by-line code analysis helps identify hidden errors and improves code efficiency by eliminating unnecessary lines.
• Improved Maintainability: White box testing begins in the initial stages of the software development lifecycle(SDLC), allowing for early bug detection and resolution. Thus, product maintenance becomes easy, leading to decreased technical debt for software developers.
• Automation Ability: Understanding the internal workings of the application allows the creation of test cases and using automation testing to run them.

2.2 Disadvantages of White Box Testing

• Less Realistic: You can only test the existing features and functionalities using the white box testing methodology. It’s not possible to detect missing or incomplete features or requirements.
• Expensive: Competent software developers and testers must understand system architecture and internal workings to design effective test cases, making it an expensive procedure.
• Rapidly Changing Code Base: Modifications in the source code often require the recreation of test cases, increasing test case overhead and wastage of time and effort.

2.3 Techniques of White Box Testing

The following are the commonly used white box testing techniques for assessing the internal structure of the software.

• Statement Coverage: The idea of the statement coverage technique is to execute every line of source code at least once during the testing process to ensure complete coverage. The formula to compute the statement coverage is:
  Statement coverage = (Number of executed statements / Total number of statements in source code) * 100
• Branch Coverage: The test scenarios that examine all the branches of the program’s control flow graph. It traverses every decision point to execute all the possible outcomes of the control flow statement at least once. The formula to compute the statement coverage is:
  Branch coverage = (Number of executed branches / Total number of branches in the code) * 100
• Path Coverage: This white box testing technique independently evaluates all the logical paths in the program, i.e., the arrangement of code statements and branches.
• Condition Coverage: It tests all the conditional statements in the code to identify and resolve logical errors. We can calculate condition coverage using the below formula:
  Condition Coverage = (Total count of conditions executed / Total count of conditions in the source code) * 100
• Data Flow Testing: It determines the flow of data within the program using the control flow graph.

3. Key Differences between Black Box Testing and White Box Testing

We have learned the fundamentals of both Black box and White box testing methods. Let us now compare them based on some important parameters and understand the key differences:

3.1 Process

The Black box testing process begins with a thorough understanding of requirements from the software requirement specification (SRS) document. Testers write test cases according to their understanding of requirements and execute them. The bugs encountered are reported to the development team for necessary corrections.

White box testing is a thorough process that begins with identifying the target component. You need to refer to the detailed design document to get a thorough with the system architecture and internal workings. The target is the smallest of the components. Afterward, a flow graph is created explaining all the test scenarios. Test cases are prepared based on this graph and executed accordingly.

3.2 Expertise Level

Black box testing is a kind of behavioral testing; therefore, testers must understand how the users will interact with the application to assess its functionality and behavior from the user’s perspective.

White box testing requires technical expertise in programming languages and frameworks, as well as knowledge of system design, data structures, and algorithms to comprehend the application’s internal design and code structure.

3.3 Program Evaluation Vs. Structural Testing

Black box testing uses the trial-and-error method to check the functionality of the program. Testers run the application multiple times to identify errors in its operation.

White box testing examines every structural code line to identify errors. After discovering an error, testers explore different ways to fix it to improve code quality.

3.4 Focus of Testing

Black box testing focuses on the external functionality and behavior of the software from the user’s point of view.

White box testing examines the structural aspects of the software, focusing on the internal code structure. The aim is to understand the software’s logic and identify code-level issues.

3.5 Test Case Design and Coverage

The test cases are presented as user stories, along with expected results, in black box testing. It tries to cover all possible scenarios to verify the software functionality.

Test cases for White box testing focus on control statements, code paths, algorithm testing, etc.

3.6 Automated Testing

Automation tools in black-box testing simulate real-world scenarios and execute test cases systematically to check user interaction. Testers use Selenium, Appium, and Katalon Studio as popular automation tools for black box testing.

Automation enhances the speed of testing complex code logic, thereby improving testing efficiency. JUnit, NUnit, and TestNG are commonly used frameworks for white box testing.

3.7 Applicability

Black box testing is performed during various stages of the SDLC to check the software’s external behavior and security vulnerabilities.

White box testing starts in the early stages of the software development process to identify flaws within the code and correct them, ultimately improving code quality.

4. When to Use Black Box Testing?

Let us look at some scenarios where black box testing is most suitable:

• Functionality and User Experience are of Utmost Importance

If you want your product to be user-friendly, black box testing can help you identify usability issues that users may encounter while interacting with the software.

• Software is Being Developed in Multiple Iterations or Versions

If you are following an iterative approach to the software development process, you should implement black box testing. This type of testing ensures that developers build the product in each iteration according to the requirements.

• For System Testing

System testing ensures your product’s end-to-end compliance with functional and non-functional requirements before software release.

5. When to Use White-Box Testing?

Now, moving towards the use cases for white box testing.

• High-Quality Code and Maintainability 

Bugs arise due to improperly written code. White box testing actively examines every line of code to ensure good code quality and maintainability.

• Applications Implementing Complex Algorithms, Data Structures, or Security Mechanisms

High-level software applications like enterprise software are built using complex algorithms and data structures. Hence, it’s important to evaluate their proper functioning, which can be done through White box testing.

• Gaps in Software Logic and Security Vulnerabilities

White box testing can best detect security vulnerabilities and code-related issues. It helps to ensure working software in the long run.

• External Dependency on APIs

White box testing helps identify and resolve software integration issues with other components and APIs. It facilitates easy and smooth integration.

6. Summary of Black Box vs White Box Testing

Parameters	Black Box Testing	White Box Testing
Definition	Software testing method without the knowledge of the application’s internal structure.	Software testing methodology where the tester is familiar with the software’s internal workings.
Other names	Functional testing, closed-box testing, and data-driven testing.	Structural testing, clear box testing, code-based testing, glass box testing, and transparent testing.
Types	Functional testing, non-functional testing, and regression testing.	Unit testing, integration testing, mutation testing, security testing, etc.
Tested By	Software testers primarily perform Black Box testing.	Software developers primarily perform White Box testing.
Test Initiation	Behavior testing according to the use requirements and functionality.	Test initiation requires design documents.
Time	It takes the least time.	It is highly time-consuming.
Programming Knowledge	No requirement for any programming knowledge.	Knowledge of programming languages is compulsory.
Automation	Difficult to automate due to the dependency between testers and developers.	Easy to automate.
Testing Focus	Expensive due to the technical expertise requirement.	Logic testing evaluates the internal structure and coding of the software.
Granularity	Low	High
Cost	Cost-effective	Difficult to automate due to the dependency between testers and developers.
Algorithm Testing Suitability	Not relevant	Most appropriate for algorithm testing.
Code access	Code access isn’t required.	It needs access to internal coding.
Outsourcing	Can be easily outsourced.	Difficulty in outsourcing.
Exhaustiveness	Less exhaustive.	Comparatively more exhaustive.
Adaptability to code changes	Code modifications could get ignored.	Adapts to the changing codebase.

7. Final Thoughts

We have tried to explain the vital concepts of black box vs white box testing methodology clearly. Both methodologies have their significance. It’s not that software needs only white box or black box testing. Both are required for successful software development. Proper planning must be done to execute both tests at the correct phase of the development process. Therefore, get thorough with every detail of the testing methods.

FAQs

What is a Real-life Example of Black Box and White Box Testing?

If we’re testing the working of a payment gateway, there will be two aspects:

1. Black box testing will check whether the payment gateway is taking the payment details correctly and allowing payment completion.
2. White Box testing will check the internal workings of the payment gateway, such as the classes, methods, and how details are getting stored in the database, etc.

What is an Example of a Black Box Test?

Take a scenario of logging into a particular website. Black box testing will evaluate whether the login function takes the username and password correctly and allows the user to log in. If the user forgets the password, does the function help to recover or set a new password?