Jest

Jest is a common test runner with a vast ecosystem. Integrating with Turborepo will lead to enormous speed-ups.

Setting up

Let's say we have a monorepo that looks like this:

Install jest into the packages where you plan on having test suites. For this example, we will have tests in web and @repo/ui:

npm install jest --workspace=web --workspace=@repo/ui --save-dev

Both the apps/web and packages/ui have their own test suites, so we'll add a test script to their package.json:

{
  "name": "web"
  "scripts": {
    "test": "jest"
  },
  "devDependencies": {
    "jest": "latest"
  }
}

Inside the root turbo.json, create a test task:

{
  "tasks": {
    "test": {}
  }
}

Now, turbo test can parallelize and cache all of the test suites from each package, only testing code that has changed.

Running tests in watch mode

When you run your test suite normally, it completes and outputs to stdout. This means you can cache it with Turborepo.

But when you run your tests in a watched mode, the process never exits. This makes a watch task more like a development task.

Because of this difference, we recommend specifying two separate Turborepo tasks: one for running your tests, and one for running them in Jest's watch mode. Inside your each package.json file for each workspace:

{
  "name": "web"
  "scripts": {
    "test": "jest",
    "test:watch": "jest --watch"
  }
  "devDependencies": {
    "jest": "latest"
  }
}

Inside the root turbo.json:

{
  "tasks": {
    "test": {},
    "test:watch": {
      "cache": false, 
      "persistent": true
    }
  }
}

You can now either run this task using global turbo as turbo test:watch or from a script in your root package.json:

turbo test

turbo test:watch