Jest: Running tests with jest seems to trigger a change in environment variables

[janpieterz]

Cross post for https://github.com/GoogleChrome/chrome-launcher/issues/86

I've created a reproduction here: https://github.com/janpieterz/find-chrome-issue

npm start works, npm test fails.

I launch a Chromeless instance and do something there, this uses chrome-launcher internally to launch a chrome instance. This relies on certain environment variables to detect the Program files folders. These _should_ be case insensitive on Windows + Node, but somehow running it with Jest seems to make them case sensitive.

This is present on:
OS Name: Microsoft Windows 10 Enterprise
OS Version: 10.0.16299 N/A Build 16299

[SimenB]

It works correctly on mac, can you describe how it fails for you?

As far as I know we only set a single environment variable, are any missing?

https://github.com/facebook/jest/blob/7743c0970e974bca166bff67099d28462ddb3187/packages/jest-cli/bin/jest.js#L12-L14

[janpieterz]

I've seen that one come through indeed. It certainly won't show up on a Mac as it's a Windows specific environment variable (and execution path).

The method called in chrome-finder.ts is here https://github.com/GoogleChrome/chrome-launcher/blob/master/src/chrome-finder.ts#L164. The error happens on the line https://github.com/GoogleChrome/chrome-launcher/blob/master/src/chrome-finder.ts#L171 where, for some reason the environment variables suddenly appear to be case sensitive when running through Jest. For example, process.env.PROGRAMFILES is not working, while process.env.ProgramFiles is.

On Windows, these are case-insensitive, and node respects this. See, for example, https://github.com/nodejs/node/blob/master/test/parallel/test-process-env.js#L93

I have no clue where to dig to find out why this changes while running in Jest. I've just verified (and pushed a fresh commit) that showcases this explicitly.

The code run is:

process.env.FOO = "bar";
console.log(process.env.FOO);
console.log(process.env.foo);

On my environment npm start outputs:

bar
bar

While npm test outputs:

  console.log random.test.js:5
    bar

  console.log random.test.js:6
    undefined

[janpieterz]

Small addition, taken a look through the Jest code and noticed two Object.assign({}, process.env, {X}).
This is done only here https://github.com/facebook/jest/blob/master/integration-tests/runJest.js#L48 and here https://github.com/facebook/jest/blob/master/packages/jest-changed-files/src/hg.js#L16

I confirmed that using an assigned env like this showcases the same behavior as above running npm test.
From the sound of the files/packages it doesn't sound like it's in the main test execution path, but it could be hinting at another dependency somewhere lower, something that perhaps launches a process with a specific env set? Or a dependency called that specifically sets process.env to something assigned.

[SimenB]

My guess is that we mess up when creating a process object to copy into the test process, see https://github.com/facebook/jest/blob/7743c0970e974bca166bff67099d28462ddb3187/packages/jest-util/src/create_process_object.js. See #4904.

Do you think you could look into a fix?

/cc @mjesun

[SimenB]

Can confirm above theory, at least:

[mjesun]

Hah, interesting! I was not aware of this behavior. It looks like env is a special object, since its constructor is neither Object nor null; and that's how it deals with this particular use cases.

The reason why this worked before is because the process.env object exposed for each test was the same one as the main process, which in turn, created leaks and unexpected behaviors (but since it's a native one, it worked as expected).

I will investigate what can we do here; but I guess a Proxy object is needed to achieve the exact same behavior.

I'm trying to get some clarification about how Node bootstraps the main context, and see if we can bootstrap any random context created via vm.createContext. This problem is, like many others (instanceof, native modules leaked...) derived from the fact that we cannot create Node contexts from scratch.

[janpieterz]

Thanks a lot @mjesun !