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As per practices of software testing services, Grey Box testing is a combination of White Box and Black Box Testing. It is also known as Grey Box analysis.
To understand Grey Box testing properly, one should be aware of White and Black box testing techniques.
BLACK BOX TESTING: In this testing technique, tester has no idea of the internal working/code of the application. The tester only test as per given requirements and front-end functionality of the system without going into depth and touching the coding part, that is why this technique is known as Black Box testing as tester is not access to the code and has a dark vision about it.
WHITE BOX TESTING: In this testing technique, tester has proper idea of the internal working/code of the application and knows about the implementation of application. Tester uses this knowledge to also test the application internally by making changes in its code as per requirement, that is why this technique is known as White Box testing as tester is aware of what's going into its code and has a clear vision about it.
As Gray box testing is a combination of both White and Black box testing but it does not mean that tester has full control of the coding part under him/her, tester has only few coding scenarios under his/her control but, yes, he/she can work internally as well as externally by following grey box technique.
An example of Gray Box Testing would be when the codes for two units/modules are studied (White Box Testing method) for designing test cases and actual tests are conducted using the exposed interfaces (Black Box Testing method).
The combination of black box and white box testing is known as grey box testing. It includes both things:
1. We check the code coverage and software features by unit test cases to validate the coverage and functionalities
2. We test the software as a black box and give all types of inputs to validate the output.
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