Document how Next and ts-jest coexist

Feature request

Is your feature request related to a problem? Please describe.

From https://github.com/zeit/next.js/issues/3663#issuecomment-385361537 and https://github.com/zeit/next.js/issues/8663, it looks like no single value for the tsconfig’s compilerOptions.jsx works for both Next.js (which requires "preserve") and Jest (which requires "react"). Those issues suggest configuring ts-jest to use a separate tsconfig.jest.json, but their guidance hasn’t made it into any actual documentation that I can find.

Describe the solution you’d like

Write a page in https://nextjs.org/docs/ saying how to get started testing.

Describe alternatives you’ve considered

• The documentation could also go in https://kulshekhar.github.io/ts-jest/user/config/.
• The solution in https://github.com/zeit/next.js/tree/canary/examples/with-jest (1) doesn’t use typescript and (2) according to https://kulshekhar.github.io/ts-jest/user/babel7-or-ts would fail to typecheck the tests.
• An even better alternative would be to improve ts-jest somehow to cope with JSX tags in its source, but that seems more work than just documenting the workaround.

[jyasskin]

I tried the with-jest example, introduced a type error, and neither npm test nor npm run build failed. A type error did cause npm test to fail when I followed the linked issues’ advice.

Even if with-jest did work for typescript, an example isn’t a complete substitute for a documentation page that describes how you intend folks to test their projects.

[Timer]

Closing per above and that we allow module: 'commonjs' on next@canary!