Babel put quite some resources into transpiling TypeScript to JS as well, and with the first-class support of babel in jest we would like to give the user the choice of using ts-jest or babel for transpiling their angular projects for jest.

Setting a babel option up and providing this to users will make this preset less opiniated and more objective, plus will also give us a clear picture which mode is faster and what problems arise with what transpilers respectively.

There are known caveats though, as babel does not type check the tests itself (similar to ts-jest's isolatedModules: true).