code coverage with nyc fails to cover all paths when using rewire@3

Expected Behavior

nyc should cover all test paths when using rewire@3 as a monkey-patching tool

Observed Behavior

When in a project that has a dependency on rewire@3, nyc will sometimes not report all the covered code that gets executed. This behavior does not occur when using rewire@2 or when using istanbul@0.4.5

Bonus Points! Code (or Repository) that Reproduces Issue

I am not entirely clear on what exactly causes this issue. It doesn’t happen all the time that rewire is being used, and load order of the files seems to matter.

Below is a repository I created that reproduces the issue in a relatively small number of files. https://github.com/bforbis/istanbul-rewire-test

Forensic Information

Operating System: macOS Sierra Environment Information:

• node version: 8.9.1
• npm version: 5.5.1

NYC issue tracker

This issue has been cross posted to the nyc github at istanbuljs/nyc/issues/747

[jhnns]

Can you provide a minimal reproducible example? 😃 That would help me to track down the bug.

[bforbis]

@jhnns I just confirmed that this has fixed the issue in my linked test repository. I also tested it on several of my private repos and saw that upgrading from rewire@2 to rewire@4 correctly preserves the code coverage from nyc, so looks like everything is working.

I’ll note that in one of my repos I did start seeing an issue with running mocha/nyc of this nature:

 "before all" hook:
     Error: global leak detected: __core-js_shared__

I don’t have a minimum reproduction I can share that caused this, but I was able to fix this issue by updating my mocha command to mocha --require babel-register. More info on that here: https://babeljs.io/docs/setup#installation