Jest requires symlinked files twice

[tmeasday]

Do you want to request a feature or report a bug?

Bug

What is the current behavior?

When requiring a file via a symlink that has already been required directly, Jest executes the file again. This is in contrast to node, which resolves the symlink's path absolutely and thus reuses the original require.

If the current behavior is a bug, please provide the steps to reproduce and either a repl.it demo through https://repl.it/languages/jest or a minimal repository on GitHub that we can yarn install and yarn test.

Reproduction: https://github.com/tmeasday/jest-symlink-repro

Install, then notice the difference between node index.js and npm test.

What is the expected behavior?

I would expect Jest to behave the same as node here.

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.

Tested with jest@20.0.4, node@8.1.0, npm@5.0.3 on OSX 10.12.5

[tmeasday]

Also, a related note--Jest appears to allow packages to require "back" over symlinks as if it is running node --preserve-symlinks: https://github.com/tmeasday/preserve-symlinks-test. Not necessarily a problem, but confusing as it behaves differently to the way your app/package likely does.