A software testing technique that evaluates an application or software product with only partial knowledge of its internal structure is called grey box testing. It is also referred to as gray box testing. Grey box testing looks for and pinpoints flaws caused by bad program usage or code structure.

Context-specific errors that pertain to web systems are frequently found throughout the grey box testing process. Focusing on every layer of any complicated system broadens the testing coverage.

Software testing techniques are of three types:

• Black Box Testing (Closed box/Functional testing/Data-driven testing).
• White Box Testing (Glass/Clear box/Structural testing/Code-based testing).
• Grey Box Testing (Gray box/translucent testing).

Gray Box Testing combines both Black and White Box Testing, enabling testing of an application’s display and source code portions. It is most useful for penetration testing and integration testing.

Comparison Of White, Black, And Gray Box Testing

Testing Coverage

Gray box testing involves partial knowledge of the internal structure. White box testing uses a known internal structure or source code, offering maximum coverage.

Black box testing is contrary to white, in which detailed design documents and internal structure are completely unknown. Only the white box supports algorithm testing.

Time Consumption

Time consumption depends on the comprehensiveness of the software testing method. White box testing is the most comprehensive in terms of internal functionality. Hence, it is a long process. Comparatively, gray box testing is faster than a white box. Black box testing is instantaneous.

Tools

Gray box and black box testing examine an operating program using dynamic code analysis tools, such as vulnerability scanning. In contrast, White box testing uses static code analysis tools.

SDLC Location

White box testing is introduced early in CI/CD pipelines since it employs source code. Gray box and black box testing are later in the SDLC since they are performed on running code.

Testing Approach

White box methodology involves a tester and developer approach, whereas black box testing also focuses on the user perspective.

Gray box testing strikes a balance between the two, removing developers’ preconceived notions about how an application should function while giving access to more knowledge than the typical user.

Examples Of Gray Box Testing

• If grey box testers have access to and know the error code table, they can thoroughly examine the error codes to explore the causes. For instance, if a website encounters “Internal server error 500”, the root cause will be a server error, as listed in the table. Instead of only reporting the problem to the developer, a tester might use this information for further evaluation and give insights to the developer.
• Suppose a gray box tester encounters issues during website analyses of links or orphan links. In that case, gray box testing techniques allow us to make the necessary modifications in the HTML code and retest in real time.
• Grey box testers can evaluate the log files to determine the error cause. Grey box tester can easily and quickly analyze application crashes, low performance, etc.

Reasons To Perform Grey Box Testing

Following are the reasons to perform grey box testing:

• This software testing technique incorporates the advantages of both white and black box testing.
• It integrates the feedback of developers and testers and enhances the quality of the final product.
• It lessens the burden of time-consuming functional and non-functional type testing processes.
• It provides a developer with adequate time to fix defects.
• Instead of testing from a designer’s perspective, a user’s point of view is considered.

Grey Box Testing Strategies

Gray box testing does not necessitate a gray box tester to have source code access to create test cases. Gray box testers can create test cases based on their understanding of algorithms, architectures, internal states, or other high-level analyses of program behavior.

Hence, to perform gray box testing:

• The black box testing technique is employed for performance testing.
• After requirement test case generation, conditions are preset, and the program is analyzed by the assertion method.

Gray Box Testing Techniques

There are four key grey box testing techniques:

1. Regression Testing.
2. Matrix Testing.
3. Pattern Testing.
4. Orthogonal Array Testing (OAT).

Regression Testing

Updating code is necessary to increase functionality or resolve security problems. Regression testing verifies whether an updated application meets the criteria.

Matrix Testing

Variables are the main subject of the matrix testing technique. In the matrix technique, all the variables are listed, their risks are assessed, and it is tested if they are used correctly and effectively.

Pattern Testing

A pattern test examines an application’s past to find patterns that may or may not lead to faults in the future. The outcomes of pattern testing can help prevent similar problems in the future.

Orthogonal Array Testing

OAT is applied to an application with a limited number of intricate inputs. It uses statistics to generate a set of test cases that provide adequate test coverage without incurring the costs associated with thorough testing.

Automated software testing tools are used in the grey box testing. Stubs and module drivers spare the gray box tester from writing the code manually.

Tools For Grey Box Testing

The available tools for gray box testing include:

• Appium.
• Burp Suite.
• Cucumber.
• DBUnit.
• JUnit.
• NUnit.
• Postman.
• RestAssured.
• Selenium.

Steps To Perform Gray Box Testing

Gray box testing involves the following steps:

1. Identify black and white box testing inputs.
2. Find outputs for identified inputs.
3. Classify major paths for the testing phase.
4. Identify sub-functions for deep-level testing of the product, software, or application.
5. Develop sub-function inputs.
6. Create outputs for sub-function inputs.
7. Execute test case for sub-function.
8. Verify desired results after execution.

For additional subfunctions, repeat steps 4 and 8 and then repeat steps 7 and 8. The test cases for grey box testing could be related to the graphical user interface, security, databases, browsers, operational systems, etc.

For instance, consider the evaluation of a website form. It sends a confirmation email to the user after form submission.

As a black box tester, the tester will supply the input of valid or incorrect email addresses for functional testing of the system.

A grey box tester with validation knowledge will perform email validation using JavaScript on the user point. With this knowledge, the gray box tester will add a new test case to his list, i.e., testing the scenarios while the browser’s JavaScript is disabled.

We can see the benefit of grey box testing in this situation. The tester could generate and run more test cases because of the additional knowledge.

Benefits Of Gray Box Testing

Other benefits of grey box testing include:

• Grey box testing offers the combined benefits of white and black box testing.
• It provides developers ample time to fix defects.
• Grey box testers do not require programming knowledge.
• It resolves disputes between testers and developers.
• Grey box testing caters to a user perspective, enhancing the overall quality of products.
• It is less expensive than integration testing.
• The clear testing goals simplify the process for testers and developers.

Drawbacks Of Gray Box Testing

• Grey box testing for connecting errors to their underlying causes can be challenging in a distributed system.
• Inaccurate output despite flawless execution of test case.
• It is not appropriate for algorithm testing.
• Limited access to the internal application structure limits code path traversal.
• Designing test cases can be challenging.
• Termination of ongoing operation due to failure of a component being tested.
• Limited internals’ visibility does not allow complete white box testing benefits.

Conclusion

Grey box testing is essential for enhancing the application security program at organizations to minimize business risks. It is advantageous as it incorporates both white and black box testing.

Compared to other software testing methodologies, this method effectively manages complicated scenarios. Instead of source code or binaries, it is based on functional specifications.

It is more efficient for functional and domain testing of web applications. Test cases in Grey box testing are created for every area, such as security, database, browser, GUI, etc.