What is the difference between Black Box and White Box Testing?

Testing undoubtedly involves numerous types, methods, and ways of verifying the actual behavior of the system against the expected behavior. Among the fundamental types are black box and white box testing, which are worth getting to know more closely. What are these types, and what checks do they entail?

Black Box Testing is a software testing method in which the functional capabilities of the software are tested without knowledge of the internal code structure and implementation details of the system. Black Box Testing primarily focuses on the input and output information of the product and is entirely based on the requirements and specifications of the software. It is also known as external testing, closed testing, or behavioral testing.

The «black box» can be any resource, whether it's an operating system, website, application, or database. This type of testing does not require knowledge and information about the architecture or structure of the product, so the checks are essentially carried out on behalf of an ordinary user.

Some of the most well-known types of black box testing include functional testing, non-functional testing, and regression testing.

The general algorithm for conducting black box testing includes:

1. verify the system's requirements and characteristics;
2. select valid input data (positive test scenarios) to check if the tested system processes them correctly. In addition, some invalid input data (negative test scenarios) are also chosen to check if the tested system can detect them;
3. determine the expected results for all positive scenarios;
4. describe test cases with selected input data;
5. execute the test cases;
6. compare the actual results with the expected ones;
7. when defects are detected, they are addressed, and retesting is performed.

As you can see, the general principles of black box testing are not a complex process that requires an overly qualified approach. Consequently, some key advantages of black box testing can be highlighted:

• it is a more efficient way to test large portions of a product due to relatively low technical testing requirements;
• it takes a relatively short amount of time;
• it does not require technical expertise or specialized knowledge;
• it has low granularity of result documentation;
• it is less resource-intensive compared to white box testing.

Disadvantages of black box testing include:

• only a limited set of input data can be tested;
• it can be challenging to design test cases if the tester does not have product specifications;
• it provides limited scope and, consequently, results.

If black box testing is testing without access to the internal workings of the product, then in contrast, white box testing is a testing method that examines the internal functioning of the system. In this testing method, the internal structure, architecture, and code of the software are checked. In white box testing, the code is accessible to testers, which is why it is also called clear-box testing, open-box testing, code-based testing, or glass-box testing. 

Some of the most well-known types of white box testing include unit testing, cyclic testing, and memory leak testing.

The general algorithm for conducting white box testing:

1. study and understand the code of the tested resource - at this stage, it is important to pay attention to the basic principles of code construction, its logic, simplicity, and, above all, security. Security is the most common goal of white box testing because vulnerabilities in the product are usually rooted in the code;
2. create and execute test cases – at this stage, the structure and correctness of the code are checked. This is usually done by writing automated test cases to check the code or through manual testing. Both automation and manual testing require a fundamental knowledge of programming.

Certainly, white box testing is distinctly different from black box testing method. Among the key advantages are:

• significant optimization of the product's code through analysis and identification of hidden errors;
• a relatively straightforward process of automating most checks;
• much more thorough checks of basic paths and connections in the product;
• the ability to start testing at the earliest stages of the software testing lifecycle, even before the front-end implementation.

Disadvantages of white box testing include:

• it is resource-intensive;
• it is challenging to execute due to high professional qualification requirements for testers;
• it requires a more limited pool of experts to perform;
• the process is time-consuming.

In summary, the key differences between these two types of testing can be summarized in the following comparative table:

In conclusion, black box testing and white box testing are two key types of testing, each with different goals: Black Box focuses on functional testing without diving into the code, while White Box delves deep into the code to eliminate vulnerabilities and potential security issues.