Mocha doesn't rethrow error from cwd-relative path js config file

[kirill-golovan]

Prerequisites

• Checked that your issue hasn't already been filed by cross-referencing issues with the faq label
• Checked next-gen ES issues and syntax problems by using the same environment and/or transpiler configuration without Mocha to ensure it isn't just a feature that actually isn't supported in the environment in question or a bug in your code.
• 'Smoke tested' the code to be tested by running it outside the real test suite to get a better sense of whether the problem is in the code under test, your usage of Mocha, or Mocha itself
• Ensured that there is no discrepancy between the locally and globally installed versions of Mocha. You can find them with: node node_modules/.bin/mocha --version(Local) and mocha --version(Global). We recommend that you not install Mocha globally.

Description

Mocha doesn't rethrow error from cwd-relative path js config file because of the incorrect comparison operator in isModuleNotFoundError function in lib/cli/config.js (should be err.code === 'MODULE_NOT_FOUND'):

mocha/lib/cli/config.js

Lines 33 to 35 in 3722201

	const isModuleNotFoundError = err =>
	err.code !== 'MODULE_NOT_FOUND' ||
	err.message.indexOf('Cannot find module') !== -1;

It will return true for the errors thrown inside config file so instead of rethrowing those errors it will try to load config file with a module-relative path:

mocha/lib/cli/config.js

Lines 48 to 53 in 3722201

	} catch (err) {
	if (isModuleNotFoundError(err)) {
	debug('parsers: retry load as module-relative path: "%s"', filepath);
	return require(filepath);
	} else {
	throw err; // rethrow

Steps to Reproduce

Create .mocharc.js:

throw new Error('foo');

module.exports = {
  spec: 'test/*.js'
};

Run it:
./node_modules/mocha/bin/mocha --config .mocharc.js

Expected behavior:
Error: Unable to read/parse /Users/me/temp_mocha_proj/.mocharc.js: Error: foo

Actual behavior:
Error: Unable to read/parse .mocharc.js: Error: Cannot find module '.mocharc.js'

Reproduces how often:
100%

Versions

• The output of mocha --version and node node_modules/.bin/mocha --version: 9.0.2
• The output of node --version: v12.13.0
• Your operating system
  • name and version: macOS 10.14.6
  • architecture (32 or 64-bit): 64-bit
• Your shell (e.g., bash, zsh, PowerShell, cmd): bash