fix dependency name clash bug

[aaronabramov]

to fix the bug i moved prettier and babel-traverse outside of node VM, so it is only required once per worker (and not in each individual test).

by doing this we'll also avoid taking the source code of our these dependencies through our resolution/transformation pipeline, which solves the issue of conflicting module names (since babel is no longer required from within the test code any more)

old description:

It seems like a pretty serious bug, i don't have a fix yet, but i'm submitting the repro in case anyone >knows what's the best way to approach it.

TL;DR:

• we use @providesModule system at fb that let's us require files directly by their names (e.g. >require('myModule111') that'll resolve to some/dir/myModule111.js)
• npm can import dependencies that have similar names
• we have a module invariant.js in fb codebase
• inline-snapshots introduced a babel dependency that also depends on invariant pakcage from >npm (https://github.com/babel/babel/blob/c7980b2b90744098ed5d67a105f8f6e7270e7cbe/packages/babel-traverse/src/path/index.js#L5)
• when we run the test, babel-traverse requires invariant that resolves to the local invarian.js >and everything breaks because our invariant.js uses flow types that aren't parseable.

[aaronabramov]

most likely i can fix it by moving require('jest-snapshot') out of the VM and require it in the outer level, but that means we'll have the same problem sometime in the future :)

[SimenB]

In general it would be awesome if we could require everything jest needs outside of the VM anyways, isn't it?
All our requires are lazy, would it still work to hoist it up?

[aaronabramov]

@SimenB yeah, ideally we should do this. in this case there's a global state that snapshots have (serializers and might be more) and it has to be required from within the VM. There shouldn't be anything that prevents us from changing that and just passing an instance of the state down to the VM

[aaronabramov]

added the fix

[SimenB]

New test fails on appveyor, not really sure why... It's complaining about invalid json in babelrc.

This should also have a changelog entry

[codecov-io]

Codecov Report

Merging #6687 into master will decrease coverage by 0.15%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #6687      +/-   ##
==========================================
- Coverage   63.71%   63.55%   -0.16%     
==========================================
  Files         235      235              
  Lines        8998     8997       -1     
  Branches        4        4              
==========================================
- Hits         5733     5718      -15     
- Misses       3264     3278      +14     
  Partials        1        1

Impacted Files	Coverage Δ
.../src/legacy_code_todo_rewrite/jest_adapter_init.js	0% <ø> (ø)	⬆️
packages/jest-snapshot/src/State.js	0% <0%> (ø)	⬆️
...ircus/src/legacy_code_todo_rewrite/jest_adapter.js	0% <0%> (ø)	⬆️
packages/jest-jasmine2/src/setup_jest_globals.js	0% <0%> (ø)	⬆️
packages/jest-snapshot/src/inline_snapshots.js	85.96% <100%> (+0.25%)	⬆️
packages/jest-cli/src/lib/update_global_config.js	72.72% <0%> (-22.73%)	⬇️
packages/jest-haste-map/src/crawlers/watchman.js	94.44% <0%> (-0.43%)	⬇️

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