fix(jest-config): Allow exactly one project

[theneva]

Summary

This fixes the issue described in #7496, where Jest ignores the project's configuration if the config's projects array resolves to exactly one project.

Fixes #7496

Test plan

I've tested that it works in my reproduction case, but I'm not sure how to write a test case for it, or why the test checked > 1 in the first place.

I'll be happy to write a test if someone nudges me in the right direction!

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[thymikee]

@SimenB I'm confused, wasn't this fixed in #5176?

[theneva]

Hmm, I'm not going to fix the broken test(s) until I know if this is necessary 😄

[SimenB]

#5176 is for object config, not a string pointing to a directory containing config.

An integration test in e2e/__tests__/multi_project_runner.test.js is failing though, @theneva mind taking a look? You can probably add a test of your own there. Take a look at https://github.com/facebook/jest/blob/master/CONTRIBUTING.md#integration-tests for some information about how the e2e tests work

[thymikee]

Yea, but this issue was marked closed as a result: #4117

[SimenB]

Oh! Haha. That has to have been an error. Seeing as this issue has a better reproduction, we should keep this open I think

[thymikee]

And nobody noticed... XD

[SimenB]

I went through and commented in that issue I closed, and closed 2 duplicates, pointing to #7496.

I'll hide shamefully in a corner 😅

[theneva]

I've added an e2e test which demonstrates the issue (breaks before the change from 1 to 0, passes after the change) in eebc494

However, the change seems to affect other stuff. Based on the other integration test that now breaks, my guess is that the root project counts towards the projects.length if no projects array is specified.

Perhaps the root project should always be counted, even when projects is set to a single non-root project? That would make us able to consistently check against > 1.

Thoughts, anyone? 😄

[SimenB]

my guess is that the root project counts towards the projects.length if no projects array is specified.

Yup, https://github.com/facebook/jest/blob/665a93eec70c4f2d7809d1848fbc8ca60cfd8361/packages/jest-cli/src/cli/index.js#L213-L234

Perhaps the root project should always be counted, even when projects is set to a single non-root project? That would make us able to consistently check against > 1.

There is some config that only applies to the root project (GlobalConfig) and not to others (ProjectConfig). I'm not sure if it's safe to ignore the difference. Maybe? Try it out and see what breaks? As long as zero projects, 1 project and multiple projects still work, we should be good

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