Question for anyone out there that has fully immersed in LWC. We are migrating our Large org from classic to Lighting (600 VF pages, several hundred javascript buttons.)  Fully analyzing what get process improvement and migration to LWC, and what gets VF styling to work for now.

The question hinges around implementing JEST testing as we build these Components.  I get the whole SDLC approach, the early testing etc.  We are putting in extensive resource to setup regression testing of the end to end process, that we will build into our CI/CD.  Having no experience with JEST and setup, or consulting partners tell us it will be 10-20% more to build the JEST tests. 

Overall i am weighing how much actually gets converted to Components from VF with backend testing, vs. specific JS component testing up front.  I know some of this also depends on how much is built into the JS for components.

Any insight from those using JEST, or those that opted not to would be a great help.