ava 4.0.1 does not work with non-native ESM, i.e., esm shim

[tcollinsworth]

@tcollinsworth AVA 4 works just fine with CJS. Being a Node.js test runner, for ESM support we rely on Node.js' standard behavior.

Originally posted by @novemberborn in #2293 (comment)

@novemberborn Upgrading ava from 3.15.0 to 4.0.1 with esm-wallaby shim for optional-chaining support throws:

SyntaxError: Cannot use import statement outside a module

[novemberborn]

I'm not familiar with that shim. AVA 3 has special handling for the esm shim and that has been removed. You'll have to register it as a CJS loader somehow.

[tcollinsworth]

AVA 3 has special handling for the esm shim and that has been removed.
You'll have to register it as a CJS loader somehow.

Any guidance on how to do that?

... WHATWG JSON modules specification are still being standardized, and are experimentally supported...
https://nodejs.org/api/esm.html#json-modules

The esm-wallaby lib is just a fork of the esm module but updated to support optional chaining (elvis operator). It works in ava 3.15.0, but fails with that error when updated to ava 4.0.1. I'm assuming this is due to removing support of esm?

ava.config.cjs

module.exports = {
  files: [
    '**/__tests__/**/*test*.js',
  ],
  ...
  require: [
    'ignore-styles',
    'esm-wallaby',
  ],
}

[novemberborn]

Correct. We used to recognize a symbol from the esm package and use it for subsequent requires, but that has been removed. I imagine there's a way to make it work like say @babel/register but I haven't looked closely.

[novemberborn]

You can specify node arguments to turn on experimental Node.js features. AVA does not do that by itself.