Split internal module registry from main module registry

[skevy]

Here's a possible fix for #1571.

When the mkdirp module is first required, it's required from jest-utils, which is required from jasmine-check.js, which is required using requireInternalModule from jest-jasmine2/index.js. Because requiring internal modules and requiring "normal" modules (e.g. in a test or within your own code) use the same module registry, when mkdirp is required by the app code, Jest already has required it (as an internal module), and thus it doesn't try to require it again and just returns it from the module registry, meaning it doesn't pick up the fs mock from our test file.

This PR splits the module registries so that conflict doesn't happen, and we can reliably use internal modules within Jest without conflicting with the test environment.

P.S. Sorry for being annoying earlier @cpojer...this is my attempt at redemption.

[cpojer]

wow, I was just messing with you but if that is what it takes to get you to contribute, that's awesome.

I also cannot believe that you actually went into jest-runtime and just made an awesome fix like this. I literally had this internal registry before but it was way more complex and I thought we didn't need it. Then I added "* Make internal registry that's persistent (?)" to my wishlist. You deserve a medal.

Would you mind also adding a test for this? It can be either an integration test in integration_tests (every folder should contain a test project and then the top level tests folder is used to call runJest (jestception)) or just directly in jest-runtime. I think I prefer integration test with a one or two line code comment on why it is necessary.

[codecov-io]

Current coverage is 90.31% (diff: 100%)

Merging #1572 into master will increase coverage by 0.01%

@@             master      #1572   diff @@
==========================================
  Files            28         28          
  Lines          1123       1125     +2   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits           1014       1016     +2   
  Misses          109        109          
  Partials          0          0          

Powered by Codecov. Last update 8b80506...430040f

[skevy]

Added integration test (with a longer than 1 line comment, sorrysss)

[cpojer]

thanks, this is great. 🎉

[github-actions]

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