Basis for writing test cases:

Friends

Normally we need 

                 i. SRS document
                ii. Usecase Document to write testcases.
to write Functional testcases.
We need Protype screens for writing GUI testcases.

Some times we will have only Functional specifications,then 
we will use only functional specifications alone to write 
testcase.

If we have still some doubts in functional flow we will see 
the design documents.

Mainly it depends on availability of documents.Generally we
will choose available documents to write testcases.

The number of testcases that can be written for application 
going to be tested will be estimated by the Test manager
with his experience.

And Also they will use some Permutations and combinations 
to calculate number of testcases.
It not possible to explain in general.If we know the 
application functionalities,then it is very easy to 
estimate the number of testcases needed to test the entire 
application. 
Normally this estimation may be less or more than actual
number of testces


Byee friends

Rajendra
rajendra.penumalli@yahoo.com
Call me:+91-9885162742
hyderabad
india