nyc test coverage not working when type:module is activated

Expected Behavior

After I’ve changed my package.json to type:module, the coverage report stopped working. All tests have passed but the report hasn’t been generated. Previously I’ve used the esm module which works fine. Someone experienced the same problem?

Observed Behavior

  186 passing (9s)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |       0 |        0 |       0 |       0 |                   
----------|---------|----------|---------|---------|-------------------

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Troubleshooting steps

• still occurring when I put cache: false in my nyc config

Environment Information

package.json

"scripts": {
    "test": "cross-env NODE_ENV=test nyc --reporter=text-summary ./node_modules/mocha/bin/mocha test --recursive",
    "coverage": "cross-env NODE_ENV=test nyc --reporter=html --reporter=text ./node_modules/mocha/bin/mocha test --recursive",
  },
  "type": "module",

[detj]

With the deprecation of node 10 coming up, I think a lot of developers (including myself) will shift to using esm modules exclusively, and it would certainly be nice if we could have direct support for it 😃

I’m one such developer. 👋

I was trying to use ava@3.15.0 with nyc@15.1.0 with "type": "module" in package.json with node@14.17.6. Got this output on running nyc ava. I have created a minimal reproduction for this as well.

  2 tests passed
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |       0 |        0 |       0 |       0 |                   
----------|---------|----------|---------|---------|-------------------

EDIT: @istanbuljs/esm-loader-hook does not appear to be workinh with node 15 and ava. I suspect it’s because the wrap-require system isn’t quite working with import

@istanbuljs/esm-loader-hook didn’t work out for me. The coverage output reported by nyc didn’t budge.

I resolved it by swapping out nyc with c8 & it worked like a charm. It works for my purposes, so I’ll stick with c8 for the time being. Though, would appreciate if nyc worked out of the box with esm as well.

[stonegray]

After some digging it appears this has been a known issue for months with no solution. There is some discussion on using c8 instead, which worked well for me in testing:

https://github.com/istanbuljs/nyc/issues/1343