Can not find jest in subpackage of yarn workspace

Question

I'm trying to refactor a Typescript project to monorepo with multiple packages (with yarn workspaces). In one of the packages (packages/compiler) I have jest installed, and have several tests. They worked before, but after refactoring I get the following error message:

Cannot find name 'it'. Do you need to install type definitions for a

test runner? Try npm i @types/jest or npm i @types/mocha

I can't seem to figure out how to get jest to work.

I have jest installed "locally" in the package with all the tests. But if I check node_modules/ after a yarn install, I can only see a .bin directory in packages/compiler/node_modules, and I can see (ts-)jest installed in the "root" node_modules. I think that I need to make sure that jest is installed in the node_modules of my packages (packages/compiler/node_modules) instead of in the root. But I can't seem to work out how to do that (the nohoist option in the root package.json doesn't work).

So my question is how do I get jest to work in my subpackage?

The root package.json:

{
  "name": "pannenkoekjs",
  "private": true,
  "workspaces": [
    "packages/*"
  ],
  "devDependencies": {
    "lerna": "^3.18.4"
  }
}

The package.json in packages/compiler:

{
  "name": "@pannenkoekjs/compiler",
  "dependencies": {
    "typescript": "^3.6.2"
  },
  "devDependencies": {
    "@types/jest": "^24.0.23",
    "jest": "^24.9.0",
    "ts-jest": "^24.1.0",
  }
}

And the jest.config.js in packages/compiler:

module.exports = {
  preset: "ts-jest",
  testEnvironment: "node",
};

Answer 1

Apparently the error wasn't about it not finding jest, but the type definitions. I have @types/jest installed, but it is installed in de "root" node_modules. And in my tsconfig.json in packages/compiler I had te following:

"typeRoots": [
    "./node_modules/@types",
    "./src/@types",
]

In other words; it was looking for type definitions in the local node_modules of that package (so packages/compiler/node_modules), while jest's type definitions were installed in the root. So adding that to the typeRoots fixed my issue:

"typeRoots": [
    "./node_modules/@types",
    "../../node_modules/@types",
    "./src/@types",
]