Hai
according to me  
In V-Model testing starts with s/w dev it self

so while preparing the URS/BRS we can write the user 
acceptance test cases
while preparing the SRS we can write the system test cases
while preparing the design we can write the integration 
test cases
while preparing the coding we can write the unit test cases

Hi Suja

I need More Explanation of V-Model

pl. Can you mail me to 
   sun_ramprasad@yahoo.com

V model:
   
     BRS                    UAT
       \                   /
        SRS            SYSTEM TESTING
          \              /
          HLD        INTEGRATION TESTING
            \          /
            LLD     UNIT TESTING
              \      /
               CODING   

Explanation:
    It is a testing model,in which both testing and 
developemont is done simultaneously.Whenever a module is 
developed it is tested immediately.

Conventional V-Model represents the development process in 
the form of a V shape. The right side of the V represents 
the testing where the systems is validated against the 
specifications defined on the left side. The meeting point 
of the V represents the actual development

Business Requirements      Acceptance Testing
       \                   /
        SRS            SYSTEM TESTING
          \              /
          HLD        INTEGRATION TESTING
            \          /
            LLD     UNIT TESTING
              \      /
               CODING   

The V-model is a graphical representation of the systems 
development lifecycle. The V-model is a software 
development process which can be presumed to be the 
extension of the waterfall model. Instead of moving down in 
a linear way, the process steps are bent upwards after the 
coding phase, to form the typical V shape. The V-Model 
demonstrates the relationships between each phase of the 
development life cycle and its associated phase of testing.


The four main process phases – requirements, specification, 
design and implementation – have a corresponding 
verification and validation testing phase.Implementation of 
modules is tested by unit testing, system design is tested 
by integration testing, system specifications are tested by 
system testing and finally acceptance testing verifies the 
requirements.

The V-model gets its name from the timing of the phases. 
Starting from the requirements, the system is developed one
phase at a time until the lowest phase, the implementation 
phase, is finished. At this stage testing begins, starting 
from unit testing and moving up one test level at a time
until the acceptance testing phase is completed.