Reproducer

Summary:

mocha does not run tests when used with import-in-the-middle as require.main === module evaluates to false.

Description:

When running mocha from ./node_modules/bin/mocha, it spawns a new subprocess, which runs ./node_modules/mocha/lib/cli/cli.js. When spawning the process it applys loaders as defined in .mocharc.json under the node-option key. When specifying the import-in-the-middle loader, the resulting command then looks like: node --loader import-in-the-middle/hook.mjs node_modules/mocha/lib/cli/cli.js.

./node_modules/mocha/lib/cli/cli.js checks if require.main === module, which is a common way to test if a (commonjs) module is being loaded from the command line. However, when using --loader import-in-the-middle/hook.mjs this evaluates to false, and the process exits with O, even though none of the tests did run.

The example here includes a single test file ./tests/simple.test.mjs, which should always fail:

• npm install
• npm run test
  • this script does not use import-in-the-middle, test fails as expected,
• npm run test:iitm
  • this script uses import-in-the-middle/hook.mjs as a loader, and does not fail

Details:

• OS: Ubuntu 22.04
• Node.js v18.18.1
• other versions, see package.json