patricklafrance/jest-monorepo

POC to test Jest monorepo setup

jest-monorepo

Usage

First install the dependencies with PNPM:

pnpm install

Then run the tests:

pnpm test

Learning

• Jest projects works pretty well for a monorepo setup.

• The command can be executed at the root and the root Jest's config file is used.

• For every monorepo project, the root config is merged with the project's own Jest config. With this setup, configuration fields like transform can be kept code per project instead of configuring a generic global transform config in the root file.

• Every project tests are run in the same process and the results are outputed as a whole in a single report.

Setup

• For Jest projects to work with a PNPM setup, Jest must also be installed at the root.

• If using a .ts configuration file for Jest, a root ts.config.json file should also be provided to configure TS.

• A jest.config.ts file cannot import ESM libraries nor used ESM assets syntax because the current implementation of jest-config hardcode the module prop to CommonJS (view https://github.com/jestjs/jest/blob/main/packages/jest-config/src/readConfigFileAndSetRootDir.ts#L118).