When a Test Case can be written in V lifecycle model?

Answer 1

The V-Shaped model is the same as the Waterfall model except that testing is a consideration throughout the development.
Each phase must be completed before the next phase begins. Testing is emphasized in this model more so than the waterfall model though. The testing procedures are developed early in the life cycle before any coding is done, during each of the phases preceding implementation.
Each stage of development is matched with its equivalent stage in testing: Requirements ó System testing, High-level design ó Integration testing, Detailed design ó Unit testing. Looking at how each stage applies to the testing of that stage might affect the way that the particular phase is approached and/or documented.
ussually it is considered that it allows for more extensive testing, as the testing is built into each phase of development, rather than as an afterthought (allows for more than black box testing).