Скачать или смотреть How to Configure jest coverageDirectory for a Project Inside a Monorepo

Learn how to set up Jest's `coverageDirectory` configuration for individual projects in a TypeScript monorepo. Discover effective solutions to avoid a common issue where coverage reports are generated at the root level instead of project-specific directories.
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A Deep Dive into Jest Coverage Configuration in Monorepos

Managing multiple projects in a monorepo can often lead to complex configurations, especially when it comes to testing. One common issue developers face is configuring Jest to output coverage reports in different directories for each project, rather than the default coverage directory at the root level of the monorepo. This guide will guide you through the configuration nuances for addressing this challenge effectively.

Understanding the Problem

Imagine this scenario: You have a Typescript monorepo with multiple packages. You've set up Jest to run tests on each package, but upon running the tests, you notice that the coverage reports are being generated at the root of your monorepo rather than in the specified directories of each respective package. This can clutter your project, making it harder to find pertinent information related to individual packages.

What's Happening?

In a typical Jest configuration for a monorepo, the root jest.config.js applies settings globally across the packages, including the coverage output directory. Therefore, if you need separate coverage directories for each package, the default setup won't suffice. Instead, you'll need to run Jest individually for each project.

Solution to Customize Coverage Directory

Key Steps to Configure coverageDirectory

Individual Package Configuration: Ensure each package has its own jest.config.js file where you specify the coverageDirectory. Here’s a basic structure for the jest.config.js file inside the server package:

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Avoid Global Jest Configuration: When you use a global jest.config.js at the root of your monorepo, every child project inherits those configurations, including the coverage directory. To allow distinct configurations for each package, avoid setting up coverageDirectory in the global file.

Run Jest Individually for Each Package: You must run Jest for each project separately so that the configurations specified in their respective jest.config.js are applied. You can do this using npm scripts in your package.json files, for example:

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Then run the command npm run test from each package directory.

Troubleshooting Tips

If you run into issues where Jest is still outputting coverage to the root:

Check Jest Version: Ensure you are using a compatible version of Jest that handles monorepo configurations well.

Clear Jest Cache: Sometimes stale cache can affect the testing environment. Clear the cache using jest --clearCache.

Double Check Paths: Ensure that the paths in your coverageDirectory are correct and relative to the current working directory.

Conclusion

Setting up Jest coverage directories in a TypeScript monorepo can be a bit tricky, but with the right configuration, you can achieve clean and organized coverage reports for each project. By keeping the configurations separate and running tests individually, you maintain clarity and efficiency in your development workflow.

Now that you have these insights, you can adapt your Jest setup to better suit your monorepo's structure, ensuring each project's coverage reports are easy to find and analyze.

Happy testing!