Mocha 6.2.0 gives error "Cannot find module esm"

[ebdrup]

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

When using esmmocha 6.2.0 gives the error Cannot find module esm, if I change nothing and run the same thing in mocha 6.1.4 everything works.

Steps to Reproduce

.mocharc.js

module.exports = {
  require: ['esm', './test/common.js'],
  recursive: true,
  timeout: 10000,
  exit: true,
  spec: './test/**/*.test.js',
  package: './package.json',
};

test/common.js

import cnf from 'cnf';
import 'chai/register-should';
import chai from 'chai';
import chaiHttp from 'chai-http';
import chaiSubset from 'chai-subset';

chai.use(chaiHttp);
chai.use(chaiSubset);

Expected behavior: [What you expect to happen]

Test run

Actual behavior: [What actually happens]

Output

> NODE_ENV=test mocha

mocha debug [spec..]

Run tests with Mocha

Rules & Behavior
  --allow-uncaught           Allow uncaught errors to propagate        [boolean]
  --async-only, -A           Require all tests to use a callback (async) or
                             return a Promise                          [boolean]
  --bail, -b                 Abort ("bail") after first test failure   [boolean]
  --check-leaks              Check for global variable leaks           [boolean]
  --delay                    Delay initial execution of root suite     [boolean]
  --exit                     Force Mocha to quit after tests complete  [boolean]
  --forbid-only              Fail if exclusive test(s) encountered     [boolean]
  --forbid-pending           Fail if pending test(s) encountered       [boolean]
  --global, --globals        List of allowed global variables            [array]
  --retries                  Retry failed tests this many times         [number]
  --slow, -s                 Specify "slow" test threshold (in milliseconds)
                                                          [string] [default: 75]
  --timeout, -t, --timeouts  Specify test timeout threshold (in milliseconds)
                                                        [string] [default: 2000]
  --ui, -u                   Specify user interface    [string] [default: "bdd"]

Reporting & Output
  --color, -c, --colors                     Force-enable color output  [boolean]
  --diff                                    Show diff on failure
                                                       [boolean] [default: true]
  --full-trace                              Display full stack traces  [boolean]
  --growl, -G                               Enable Growl notifications [boolean]
  --inline-diffs                            Display actual/expected differences
                                            inline within each string  [boolean]
  --reporter, -R                            Specify reporter to use
                                                      [string] [default: "spec"]
  --reporter-option, --reporter-options,    Reporter-specific options
  -O                                        (<k=v,[k1=v1,..]>)           [array]

Configuration
  --config   Path to config file           [string] [default: (nearest rc file)]
  --opts     Path to `mocha.opts`        [string] [default: "./test/mocha.opts"]
  --package  Path to package.json for config                            [string]

File Handling
  --extension, --watch-extensions  File extension(s) to load and/or watch
                                                           [array] [default: js]
  --file                           Specify file(s) to be loaded prior to root
                                   suite execution     [array] [default: (none)]
  --ignore, --exclude              Ignore file(s) or glob pattern(s)
                                                       [array] [default: (none)]
  --recursive                      Look for tests in subdirectories    [boolean]
  --require, -r                    Require module      [array] [default: (none)]
  --sort, -S                       Sort test files                     [boolean]
  --watch, -w                      Watch files in the current working directory
                                   for changes                         [boolean]

Test Filters
  --fgrep, -f   Only run tests containing this string                   [string]
  --grep, -g    Only run tests matching this string or regexp           [string]
  --invert, -i  Inverts --grep and --fgrep matches                     [boolean]

Positional Arguments
  spec  One or more files, directories, or globs to test
                                                     [array] [default: ["test"]]

Other Options
  --help, -h     Show usage information & exit                         [boolean]
  --version, -V  Show version number & exit                            [boolean]
  --interfaces   List built-in user interfaces & exit                  [boolean]
  --reporters    List built-in reporters & exit                        [boolean]

✖ ERROR: Unexpected identifier
npm ERR! Test failed.  See above for more details.

Reproduces how often:
100%

Versions

• The output of mocha --version
  ash: /usr/local/bin/mocha: No such file or directory

and node node_modules/.bin/mocha --version:
6.2.0

• The output of node --version:
  v10.16.3

• Your operating system

  • name and version:
    macOS Mojave, version 10.14.6

  • architecture (32 or 64-bit):
    64

• Your shell (e.g., bash, zsh, PowerShell, cmd):
  standard OSX

• Your browser and version (if running browser tests):

• Any third-party Mocha-related modules (and their versions):

  "chai": "4.2.0",
  "chai-http": "4.3.0",
  "chai-subset": "1.6.0",

• Any code transpiler (e.g., TypeScript, CoffeeScript, Babel) being used (and its version):
  esm v3.2.25

Additional info:

If you globally install mocha ant try to run tests it gives the error Cannot find module esm

[juergba]

I suppose you have been installing the esm package.
duplicate see #3975

[FossPrime]

The solutions to this are here: sveltejs/kit#612 (comment)

Tl;dr;

• use an experimental extension resolving feature OR
• Change your extensions and add index.js to all your directory auto resolutions