jest with esm is running in shared scope

[dnalborczyk]

node v10.5.0
esm: v3.0.62
jest: v23.3.0

problem: jest test files are running individually in their own scope, though when to-be-tested-modules files are being loaded with esm the scope is being shared.

repro:

https://github.com/dnalborczyk/esm-jest-repro/tree/jest-scope

edit: added repro

[jdalton]

Ah yes, this would make sense because we are sharing the context 😋
It can be adjusted to be individualized though.

Update:

Ok so in digging into this a little more the issue isn't about scopes or contexts it's about shared Module._cache data. The esm loader will share cache data per identically configured instance. I can see now though that each instance should have their own module cache.

Update:

Ok so digging into it even more we don't share Module._cache between instances explicitly it's the fact that our internal Module._cache is initialized with that of CJS (the real Module._cache). Jest must not be clearing the real Module._cache which is why ours is allowed to persist.

Deferring to the builtin CJS cache is a good thing that helps with CJS interop. I don't want to remove that so instead I can detect if esm is running in jest and start fresh in that case only. When running in jest there is a global free variable jest that I can detect.

[dnalborczyk]

incredible work!! thanks for the updates! much appreciated!

the bug is fixed in master, tests are passing nicely! 🎉 🎉 🎉

[jdalton]

v3.0.63 is released 🎉