paularmstrong / jest-multi-project-example

Yarn Workspaces with Jest Multiple Projects

Setup

1. yarn to install dependencies and link workspaces
2. yarn test to ensure tests work correctly

Reproducing The Issue

In this example, we would like to see the following happen:

1.Run yarn test --findRelatedTests --listTests projects/bar/bar.js (test is a package script shortcut to jest)

Expectation

We should expect to see the following files as related in the output:

projects/bar/__tests__/index.test.js
projects/foo/__tests__/index.test.js

Actual results

Jest does not appear to resolve related changes across project configurations and we do no receive any listed tests.

Alternatively

If we run yarn test --findRelatedTests --listTests projects/bar/index.js, we do receive only the file for the direct project, bar.

projects/bar/__tests__/index.test.js

Why this is problematic

This is a problem because if we are in a sufficiently large project with many workspaces and many interdependencies, we may make a change to one file in a single workspace and expect to be able to run only the related tests for that change, but none will be run.

We could argue that we should just run all tests, but this can take too long (15+ minutes) to realistically ask people to do every time they make a change.