Tell me about advantages of test design document over test plan?

Please reply only after reading my question atleast two times...

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Brijesh Jain
brijesh.tester@yahoo.co.in
http://softwaretestingexpertise.blogspot.com

Hi,
I don't think there is any advantage or disadvantage of test design document over the test plan as such, because i believe this two are completely different docs which are required for different purpose.

Test Plan involves the entry/exit criteria for the Test project. Also it involves the budget, strategy etc.

Test Design doc is a building block for the Test case. It involves what specific test techniques to be followed. What sort of Information we expect the Test case to reveal? what is the cost of the test case and what level of maintainability and repeatable test case we need to design for the AUT.

Thanks.
Please let me know your views.