Grey box testing is the combination of black box and white box testing. Intention of this testing is to find out defects related to bad design or bad implementation of the system.
In gray box testing, test engineer is equipped with the knowledge of system and designs test cases or test data based on system knowledge.
For example, consider a hypothetical case wherein you have to test a web application. Functionality of this web application is very simple, you just need to enter your personal details like email and field of interest on the web form and submit this form. Server will get this details, and based on the field of interest pick some articles and mail it to the given email. Email validation is happening at the client side using Java Scripts.
In this case, in the absence of implementation detail, you might test web form with valid/invalid mail IDs and different field of interests to make sure that functionality is intact.
But, if you know the implementation detail, you know that system is making following assumptions
- Server will never get invalid mail ID
- Server will never send mail to invalid ID
- Server will never receive failure notification for this mail.
So as part of gray box testing, in the above example you will have a test case on clients where Java Scripts are disabled. It could happen due to any reason and if it happens, validation can not happen at the client site. In this case, assumptions made by the system are violated and
- Server will get invalid mail ID
- Server will send mail to invalid mail ID
- Server will receive failure notification
Hope you understood the concept of gray box testing and how it can be used to create different test cases or data points based on the implementation details of the system.
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