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I've read that if a requirement can't be verified by black-box testing or inspection, then it's not a requirement, but a design specification.

I'm building a software that makes processing with on images acquired by a camera, and the processing itself should be verified because it is essential for producing the right image presented to the end user.

However it is very difficult to test this in black-box, even in gray-box, so I wonder if it should be listed as a software requirement? If yes, then is it OK for my software verification to have it verified in white or gray-box testing?


PS: I'm building medical device software, thus following IEC 62304 standard, that specifies that my software requirements shall be verified through system testing.

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What distinction are you drawing between 'requirement' and 'design specification'? –  vincebowdren Jul 29 '13 at 15:37
    
I use 'requirement' as "functional requirement", i.e. a capability that the software must present. A design specification is the way the software is built in order to implement this capability –  CharlesB Jul 29 '13 at 15:40

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up vote 9 down vote accepted

I've read that if a requirement can't be verified by black-box testing or inspection, then it's not a requirement, but a design specification.

I don't think that's true. There are plenty of requirements which are difficult-to-impossible to test with black-box techniques; for example, a client-server application might have a requirement that all communications between client and server is encrypted - but black-box testing can't see the communications at all. But that doesn't stop it being a valid requirement.

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Thanks for your answer; so gray-box testing (by inspecting communication logs, for example) can be considered as a valid requirement verification? –  CharlesB Jul 29 '13 at 16:12
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Certainly. It's a bit of a myth that you can do everything with black-box testing, and it puts artificial limits on what testing you should be doing, and how you should be doing it. –  vincebowdren Jul 29 '13 at 16:23

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