What is Gray-box Testing?

Gray-box testing is a software testing technique that seeks to optimize the testing process by exposing some of the software's inner workings to test case designers.

Black-box testing can be time-consuming, while white-box testing requires testers to read and write code. Gray-box testing aims to reduce the testing process's time and effort without requiring testers to be programmers. It exposes the workings of specific modules, algorithms, and software components to the test case writers so that they can focus the testing effort on the right areas.

Gray-box testing is often thought of as a blend of black-box and white-box testing; however, we believe it has an independent existence.

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A Real-world Example of Gray-box Testing

Let's say that we are developing a task management application in which tasks can be recurring. For example, you can create a "Send Weekly Update" task to repeat every Friday at 3 PM.

The task form has a "Repeats" tab that has the following form elements:

Starts On 1-April-2020 2:00 PM
Time Zone Central European Time
Repeats Every Week
Repeats On Mon, Wed, Friday
Ends On 1-April-2021

If we did black-box testing of the repeating functionality, we would have all kinds of tests; probably hundreds of them. If we did white-box testing, we would be examining the condition and path coverage of the back-end code.

Both would be very time-consuming.

Imagine if the software developers told our testers that they use a popular 3rd party library that handles the front-end form and the back-end code. This information will significantly transform the way we will do testing of the "Repeating" functionality. Because we know that we are using a popular and well-accepted 3rd party library that will not have significant bugs, we will most likely have about ten test cases and still be assured of the software's quality.

Partial knowledge of the inner workings of the software has helped in significantly reducing the testing effort.

Grey box testing Techniques

Matrix Testing

Matrix testing is a technique that prioritizes testing based on the matrix of all the variables in the system, their constraints, and associated technical and business risks.

Suppose we have developed a web-based service that can convert an HTML document to PDF using an API. The matrix would look like this:

From the matrix shown above, we can conclude that PDF documents' scaling is more important than testing its margin. The matrix has helped us prioritize our testing.

Regression Testing

Regression testing verifies that modifications done in a software system have not affected it adversely.

Gray-box regression testing uses inside knowledge to determine the regression testing strategy. For example, if you find from your source control system that an enhancement has not affected any other source file, you can safely skip regression testing. If you discover that a shared library has been significantly modified, your team will have to test the entire application.

Pattern Testing

Pattern testing tries to optimize testing by finding patterns in defects from historical data.

In gray-box testing, you further investigate the defects to find out the root cause. Based on this data, you can then improve your test cases.

For example, let's say that you find that your project management application had many bugs related to scheduling when two or more resources are assigned to a task in the previous release. If you dig deeper, you may find that the problem happens when resources work in different time-zones and all the test cases failed because they all used the same time-zone class library that had the defect.

The solution could be to introduce unit testing in the time-zone library or design some basic black-box tests which, if failed, aborts testing for the scheduling module to save time.

Orthogonal Array Testing

Orthogonal Array Testing is a statistical testing technique that aims to provide maximum coverage with minimum test cases in software systems.

This method is beneficial for complex software applications where black-box testing will be inadequate.

Advantages of Gray-box Testing

  • You get more coverage with fewer test cases, which means you require fewer testing resources, and your developers get more time.
  • Testers are not required to have high programming skills.
  • It is unbiased and avoids conflicts between testers and developers.
  • It is non-intrusive.

Disadvantages of Gray-box Testing

  • Test cases are challenging to design.
  • It depends on good design documents (or helpful developers).
  • Difficult to implement in distributed systems.
  • Coverage may not be adequate.