---
title: Jest example
sidebar_label: Jest
---

import AddDepsTabs from '@site/src/components/AddDepsTabs';
import HeadingApiLink from '@site/src/components/Docs/HeadingApiLink';

<HeadingApiLink to="https://github.com/moonrepo/examples/blob/master/.moon/tasks/node.yml#L83" />

In this guide, you'll learn how to integrate [Jest](https://jestjs.io/) into moon.

Begin by installing `jest` in your root. We suggest using the same version across the entire
repository.

<AddDepsTabs dep="jest" dev />

## Setup

Since testing is a universal workflow, add a `test` task to [`.moon/tasks/**/*`](../../config/tasks)
with the following parameters.

```yaml title=".moon/tasks/jest.yml"
tasks:
  test:
    command:
      - 'jest'
      # Always run code coverage
      - '--coverage'
      # Dont fail if a project has no tests
      - '--passWithNoTests'
    inputs:
      # Source and test files
      - 'src/**/*'
      - 'tests/**/*'
      # Project configs, any format
      - 'jest.config.*'
```

Projects can extend this task and provide additional parameters if need be, for example.

```yaml title="<project>/moon.yml"
tasks:
  test:
    args:
      # Disable caching for this project
      - '--no-cache'
```

## Configuration

### Root-level

A root-level Jest config is not required and should be avoided, instead, use a [preset](#sharing) to
share configuration.

### Project-level

A project-level Jest config can be utilized by creating a `jest.config.<js|ts|cjs|mjs>` in the
project root. This is optional, but necessary when defining project specific settings.

```js title="<project>/jest.config.js"
module.exports = {
  // Project specific settings
  testEnvironment: 'node',
};
```

### Sharing

To share configuration across projects, you can utilize Jest's built-in
[`preset`](https://jestjs.io/docs/configuration#preset-string) functionality. If you're utilizing
package workspaces, create a local package with the following content, otherwise publish the npm
package for consumption.

```js title="packages/company-jest-preset/jest-preset.js"
module.exports = {
  testEnvironment: 'jsdom',
  watchman: true,
};
```

Within your project-level Jest config, you can extend the preset to inherit the settings.

```js title="<project>/jest.config.js"
module.exports = {
  preset: 'company-jest-preset',
};
```

> You can take this a step further by passing the `--preset` option in the [task above](#setup), so
> that all projects inherit the preset by default.

## FAQ

### How to test a single file or folder?

You can filter tests by passing a file name, folder name, glob, or regex pattern after `--`. Any
passed files are relative from the project's root, regardless of where the `moon` command is being
ran.

```shell
$ moon run <project>:test -- filename
```

### How to use `projects`?

With moon, there's no reason to use
[`projects`](https://jestjs.io/docs/configuration#projects-arraystring--projectconfig) as the `test`
task is ran _per_ project. If you'd like to test multiple projects, use
[`moon run :test`](../../commands/run).
