What Is Grey Box Testing? Definition, Techniques and Pros and Cons

Updated June 20, 2023

If you're seeking employment as a software developer or engineer, your interviewer may ask questions about specific concepts or skills. Grey box testing is a popular topic and an important skill for software developers, so it's important to know how to answer if you're asked about the process. Understanding what grey box testing is and why it's important can help candidates formulate more effective answers to impress a potential employer and showcase their proficiency.

In this article, we define grey box testing, describe its importance, explore techniques and examine pros and cons.

What is grey box testing?

Grey box testing is a software debugging method that combines two other types of testing for a more complete testing process. The other two types are:

White box testing: White box testing is an internal testing method that allows developers to verify the internal codes, integrations and infrastructure of software with proprietary external systems. It's often an automated process and provides instant feedback on any bugs or vulnerabilities in the software.
Black box testing: Black box testing is a similar testing method that allows developers to test software without any prior knowledge of the software's internal machinations or code. Instead, the tester observes the software's primary functions and outputs, analyzing the software to determine its response to specific user interactions and other factors.

Grey box testing combines these two methods, allowing developers to test software functionality, security and quality simultaneously with partial internal knowledge of the software. Knowing how to perform a grey box test and black and white box testing can be a significant professional advantage for job candidates, as employers may seek developers who understand the complete testing process and all methods.

Why is grey box testing important?

Grey box testing can be incredibly important for software testing for many reasons, including:

Combines the benefits of black and white box testing: Grey box testing has the advantage of combining methods from both white and black box testing, getting the best of both methods and allowing for a more robust and efficient testing process.
Tests front and back-end development: Grey box testing allows developers to test both sides of a software application for a more complete analysis of potential vulnerabilities and errors.
Serves as a key skill for employment: Grey box testing is also important because it can help make more desirable job candidates as employers look for more versatile employees.
Identifies specific vulnerabilities from a user perspective: Grey box testing allows testers to identify more specific vulnerabilities by shifting the testing perspective from developer to user or attacker.

Techniques for grey box testing

Grey box testing consists of four different techniques, which include:

Matrix testing

The primary testing method in grey box testing is matrix testing. This method requires that developers define all the variables that exist in their proprietary programs. The variables are typically responsible for errors, functionality and other factors that can affect the testing process. By identifying and understanding each variable in the software, the developers performing tests have a general idea of what to expect. Fewer surprises and a healthier understanding of the software's internal structures can help reduce testing time and improve overall accuracy.

Regression testing

Another method developers use is regression testing, which compares previous software changes to the functionality of the software's current iteration. This allows the developer to learn whether previous changes have caused any regression to occur in the newest software iteration. By identifying potential regression, developers can identify those specific changes that caused errors or reduced functionality and address them more quickly by isolating them in the change logs.

Pattern testing

Pattern testing is another grey box technique that tests the historical data of previous system errors or software defects. Developers use pattern testing to determine why a particular error or defect occurred in historical iterations of the software to isolate and remedy those issues. This grey box method allows for a more thorough testing process of historical errors to minimize the reappearance of those issues in new software iterations and reduce the total number of errors or defects in the final product.

Orthogonal array testing

Orthogonal array testing is a grey box technique that uses an orthogonal array. This is a table that contains different entries from a fixed, finite group of common symbols, like numbers. Orthogonal array testing uses these arrays to create test cases, where developers can test specific functions within the software to identify and isolate more specific problems or defects. The method maximizes the test coverage for each software iteration and can help save time by minimizing what needs testing.

Pros and cons of grey box testing

While grey box testing is a popular testing method for developers, it does have both pros and cons to consider. Here are some examples:

Pros

Here are some pros of grey box testing:

Saves time: Grey box testing can save developers time by providing four techniques for maximum testing coverage.
Combines the best of black and white box testing: Grey box testing also combines the best aspects of black and white box testing for a more complete testing experience with greater accuracy and specificity.
Uses a different perspective: Grey box testing allows testers to test the software from the perspective of an attacker or an actual user, providing a different perspective that can yield valuable information.
Allows for testing prioritization: Grey box testing allows the developers to prioritize specific tests or testing parameters to help minimize testing times and address errors or defects more effectively.

Cons

Here are some cons of grey box testing:

Doesn't give testers access to source codes: Grey box testing doesn't typically give the testers access to the application's source code, which means they can miss potential vulnerabilities or errors.
Is potentially redundant: Grey box testing may prove redundant for testers if any similar test cases have already occurred during previous testing phases, causing delays.
Can miss certain program paths: Grey box testing can miss certain program paths in the testing process because manually testing each one is typically impractical and too time-consuming for development teams.