Black Box and White Box Testing Inside Out

Everyone would agree that new applications and software solutions should be tested. So how to do the testing right? There are three software testing methods: black box testing, white box testing, and also the gray box testing method. In the black box method, the subject of the test, the internal structure, and the implementation are not known to the tester. In white-box testing on the contrary. Gray box testing is a combination of both testing methods. Which one is better?

Before we answer this question, we need to explain what black box and white box testing is. The black one resembles watching a black box on the outside — we can see shape and color, but we don’t have a clue what’s inside. Things like the code and the architecture of the program are hidden inside.

The software tester doesn’t need to know its internal workings. The tester is aware of what the software is supposed to do but not how. All he/she cares about is whether the functionalities follow the documentation. The tester enters the input parameters and checks if the output generated by the system is correct.

This way we evaluate the particular response of the system to expected and unexpected actions of users, time of their reactions, UI/UX, server, database, dependencies, and so on.

What is Black Box Testing?

The black box testing reveals how the software operates from the end-user perspective. Testers, just like end-users, expect to receive an appropriate response to their requests. They can check if the system performs as intended. The role of the tester in a black box testing method is to prepare test scenarios — positive and negative. This testing method can be applied to almost every software like a database, an application, a website, or an operating system. Black box testing is also referred to as behavioral, closed-box, opaque-box, specification-based, or eye-to-eye test.

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What is the Purpose of Black Box Testing?

This method shows the functionality of the system. It is important because we can test the system against external factors that might cause application failure. Black box testing is critical during testing system integration, regression testing, and software development. Almost all applications are tested by both black and white box testing methods.

Black Box Testing Popular Techniques

The well-known black box testing techniques include:

• Decision table testing — it’s a visual table representation for clarifying which actions to perform depending on conditions.
• Boundary value analysis — it’s a testing method in which tests include representatives of boundary values in a range.
• Error guessing — it’s a testing technique in which finding bugs in programs are based on experience in prior testing.
• Equivalence partitioning — this testing technique is about dividing a possible input into groups called “partitions”, and test one input from each partition.
• State transition — it’s either a table or a graphic diagram (UML) in which the inputs include the current state and the outputs that include the next state.
• Cause-effect graph — a directed graph that replicates a set of causes to a set of effects.
• Domain analysis — it’s the process of checking related systems in a domain in order to find their common and variable parts,
• User story — it’s an informal description of a system feature written by an end-user.
• Use case — it’s a list of actions that define the interactions between an actor (human or an external system) and a system in order to achieve a goal.

Black Box Testing Benefits

The important advantage of black box testing is that a tester does not need to have development skills in knowledge.  In this method the important advantages are:

• the low complexity of tests,
• small chance of false positives,
• tests can be executed by a non-technical person,
• test cases can be designed immediately after the completion of specifications,
• some techniques help to detect “edge cases” errors more often.

Black Box Testing Drawbacks

One of the biggest drawbacks of black box testing is the difficulty of detecting the reason for the error hidden in the code. There are several cons, for example:

• it’s hard to automate,
• difficult to design without having clear functional specifications,
• it’s practically impossible to track all user paths,
• it’s hard to evaluate test coverage,
• there is a lack of opportunity to test individual code parts,
• tests are conducted at a low scale.

What is White Box Testing?

It’s time to ask what is a white box testing? Unlike black box testing, a tester comprehends the code of the program. The second method is usually conducted by the developer on his own but could be done by a skilled tester too. White box testing examines the internal functioning of the system.

A tester has full access to source code, architecture, and configuration. He/she can check a particular fragment of code instead of testing full functionalities. White box testing reveals the exact place and cause of the flaw. A difficult thing to achieve in black box testing.

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By conducting black and white box testing we can detect errors and find out a cause of bugs. It reveals issues like broken paths, security, or data problems. On the occasion, white box testing optimizes fragments of the code. Unfortunately, both testing methods are very much time-consuming. Especially white box testing! Looking for a single, incorrect loop in code could be a challenge! White box testing is also called a glass box, clear box, transparent box, or codebase testing.

White Box Testing Benefits

There are many benefits of white box testing. The biggest advantages are:

• possibility to check only a necessary fragment of the code or the whole system,
• tests detect a root cause of the error,
• allows designing/creating unit tests,
• allows finding hidden errors,
• it enables optimization of the code,
• tests are conducted by an experienced tester with vast technical knowledge, which can speed up the testing process significantly,
• reduces/eliminates communication cost between developer and tester.

White Box Testing Drawbacks

Except for the obvious benefits, there are some issues like:

• limited coverage, since only a selected number of test scenarios is performed,
• planning problems, since the test cases are difficult to design,
• inefficient testing, since some conditions might not be tested,
• time-consuming and expensive, as it requires a great effort to test a larger application fully,
• blind coverage, since the tester cannot target specific code segments or error-prone areas.

Read also: How to Align Communication Between Software Testers and Software Developers?

Differences Between White and Black Box Testing

These are key differences between black and white box testing:

Black box testing	White-box testing
The tester does not have knowledge about the internal structure of the program.	The tester is aware of the internal structure of the application.
Knowledge of coding is not required.	An expert tester with extensive experience or a developer is needed.
Knowledge of implementation is not required.	Knowledge of implementation is necessary.
Tested by software testers, end-users.	Conducted by software developers and testers.
Functional test of the software.	Structural test of the software.
External software testing.	Internal software testing.
Testing the complete functionality of the system and its behaviour.	Logic testing of the software.
The higher levels of testing of software.	The lower levels of testing.
Not suitable for algorithm testing.	Suitable for algorithm testing.
The least time-consuming when it comes to design tests	Mostly time-consuming when it comes to design tests.
Focused on an external or end-user perspective.	Focused on code structure, paths, and conditions.

Gray Box Testing

This method is a compromise. Gray box testing combines both white and black box testing techniques. The tester has limited knowledge of the system and internal applications. Only the output is tested in gray box testing. It is often used for extended system testing, integration, and penetration testing.

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Conclusion

Black box testing can be performed by people who are not developers. However, this type of testing sometimes fails to deliver information about the cause of the error in the code. If so, it is better to use white box testing. Performing this testing requires a basic knowledge of the developer’s skills.

The question of which one is better is the wrong question. There are problems that cannot be solved using only one technique. In that case, both testings take place – these methods complement each other. Companies like CSHARK successfully combine both black box testing and white box testing.

The reliable software developer partner uses all testing methods available to verify the functionalities of the customer’s application. Employing both kinds of testing has a positive impact on software product development. This way testers can achieve a complete “100%” inspection of software application.