All You Need to Know About Black Box Testing and White Box Testing

There are several types of testing in software testing. It is important for the tester to know when to implement which testing method.

Black box testing and white box testing are two topics that are often a cause of confusion. Both these testing methods are necessary for the successful delivery of software.

In this article, you will learn in detail about black box testing and white box testing. What is black box testing? Black Box testing is a method of testing software wherein the functionalities of the software or web applications are tested without any knowledge of the internal code structure or paths. 

How does black box testing work?

1. The tester selects a function and gives an input value to check for functionality. 
2. The tester then creates test cases with selected inputs such as decision table, all pairs test, equivalent division, cause-effect graph, error estimation, etc. 
3. Test cases are constructed around what the application is supposed to do. They are generally drawn from descriptions of the software, such as specifications, requirements, and design parameters.
4. The tester chooses both valid and invalid inputs (for both positive and negative scenarios). This is to ensure that the software processes the positive ones and detects the negative ones. 
5. The tester sets the expected outputs for all the inputs and then executes the tests to see if it gives the expected output. If it does, then the software has passed the test; if not, it has failed. 
6. The bugs or defects are fixed in the process and re-tests are conducted. The testing team reports it to the development team and proceeds to test the next function.

Black Box testing is also called Behavioral Testing. The Black Box test can be performed on any software, website, or custom application.

Among the several types of Black Box testing, the following are significant.

1. Functional testing: As the name indicates, it involves the functional needs of a system. 
2. Non-functional testing: This is where the performance and usability of the software are tested.
3. Regression testing: It is performed after any upgrades or maintenance to see if the new code has in any way impacted the existing code.
4. Decision table testing: A matrix is created placing the causes and effects in a decision table. Each column yields a unique combination.
5. Equivalence class testing: This is used to reduce the number of (test) cases to an optimum level and maintain considerable test coverage.
6. Boundary value testing: This focuses on the values at boundaries. This technique tests whether the system accepts values of a certain range.

What is white box testing?

White box testing is a software testing technique that tests the internal structure and coding of a software to verify the input-output flow and to improve the design, usability, and also security of software. Since the code is visible to testers, it is called a White box or Open box, or Clear box testing. One can apply White-Box testing at the unit, integration, and system levels of the testing process.

Types of white box testing

Several testing types fall under White Box testing used to assess the usability of a software program.

Unit testing – Unit testing is done on each unit of code as and when it is developed. In this type of testing, bugs are identified early on and are therefore easier to fix. 

Testing for memory leaks – This type of testing is extremely useful in slow-running applications, as memory leaks are responsible for slow-running applications.

White box penetration testing – In this type of testing, the tester has complete information, right from the source code of the application to the server that it runs on. Thus, it is easy to troubleshoot from various angles to identify security threats. 

White box mutation testing – This involves developing the best or the ideal coding technique for expanding and developing a software solution further. 

Why do we need white box testing?

We need white box testing for: 

1. Addressing any broken paths in the coding process
2. Addressing internal security leaks or holes
3. Verifying the inflow of inputs through the code
4. Conditional loop functionality
5. Testing every function and statement individually

In white box testing, the working flow of an application is verified. A series of preset inputs are tested against expected outputs; when the expected output is not produced, there are bugs, and those bugs are resolved.

Methods of white box testing include two important steps- understanding/comprehending the source code and creating test cases and executing them.

The tester should have a strong command over the application used in the coding as well as the security of the software. The tester usually looks for security issues and addresses them. 

Also, the source code is tested for structure and proper flow by writing more code. In this process, the developer usually creates small tests at each stage to check the flow of each of the series of processes.

White box testing techniques 

Among the techniques of white box testing, Code Coverage Analysis is an important one. It helps identify those areas of a software program that are not exercised by test cases. Those untested parts are then tested by a code, thus raising the quality of the software.

Statement coverage requires every statement in the software to be tested at least once while the testing process is carried out. Branch coverage covers every possible path including loops in the software. 

There are other techniques such as condition coverage, multiple condition coverage, control flow testing, and data flow testing.

How do you perform white box testing?

Testers employing white box testing typically know the source code and create test cases and execute. Understanding the source code involves a good working knowledge of the programming languages used in the software. Besides, the tester should be aware of the secure coding practices as well, in order to identify security issues and prevent attacks. Also, the tester would develop tests for each process. More often than not, this is done by the developer as it requires a strong command over the code. Other methods employed are manual testing and trial and error testing.

Merits of white box testing:

• Optimization of code by identifying hidden errors
• Thorough testing as each path and statement are covered
• Testing can start even without the graphic user interface
• Ease of automation 

Demerits of white box testing:

• It is complex, expensive, and time-consuming
• It requires a lot of detailing which if not performed can lead to production errors
• It requires professional resources and in-depth knowledge of software
• It is detailed and each statement or path is covered. Unless one has adequate time and resources at hand, it cannot be performed successfully

White box testing is complex on the one hand but thorough and detailed on the other. While small applications may be tested in minutes, larger applications may even take weeks to fully test. White box testing is done on software applications as it is being developed and once again after any modification.

In conclusion

As a software tester, you must know and understand the differences between these two types of software testing methods. You need to think about the final product and strategically apply the testing method so as to ensure that the software provides the best user experience.

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Rajakrishnan B.

Associate VP of Technology, leads the design and development of innovative and accessible web solutions for publishing and eLearning clients. With over 20 years of experience in the ITES industry and a strong background in project management, automation, quality assurance, and offshore collaboration.