Waterfall model:
in this type of model the flow is sequential starting from 
the planning ,design,coding and after that testing is put 
into effect .so the testing is after the coding only and 
not before that
V-Model:
in this model the testing starts after business 
requirements  is finished and furnished 
and testing continues in paralled with the coding
so that we can eliminate  error in the earlier stage

In the waterfall model we have single phase testing.
That should be after completion of code.

In the v-model we have mutiple phase testing,in every phase 
we should use testing.

water fall model is most expensive model.in this model, 
each phase has to be freezed to move to next phase 

V model is mapping between development  and testing process.
here both team involves simultanious .
main benefit is we can reduce the test design time and also 
more flexibilty.