I remember having trouble with this recently. No specific examples to cite because I gave up and nuked the project, but support for ESM is experimental in Jest. I literally just couldn't get it to work with ES6. I remember thinking I would have to compile to CJS so jest would work.

edit: just found this, which seems to confirm my anecdotal xp of esm in jest being weird https://github.com/facebook/jest/pull/11529#issuecomment-102...