Using Istanbul and Mocha to cover ES6 code

Question

I have Node code, written in ES6, that I test by issuing mocha --harmony. Tests are fine - everything works.

Now I want to add coverage and istanbul to the mix, but I keep getting errors on the first arrow function encountered:

No coverage information was collected, exit without writing coverage information
c:\Users\Guy\Code\alpha-dev\tests\helpers.js:12
    setTimeout(() => {
                ^
SyntaxError: Unexpected token )
    at exports.runInThisContext (vm.js:73:16)
    at Module._compile (module.js:443:25)
    at Module._extensions..js (module.js:478:10)
    at Object.Module._extensions..js (c:\Users\Guy\Code\alpha-dev\node_modules\istanbul\lib\hook.js:101:13)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Module.require (module.js:365:17)

Here's what I tried:

1. Installed istanbul-harmony (from git://github.com/gotwarlost/istanbul.git#harmony) as my dev dependency.
2. Running the following command: "./node_modules/.bin/istanbul" cover "./node_modules/mocha/bin/_mocha" -- --harmony tests -R spec
3. Combinations on flags for both istanbul and _mocha

How can I run istanbul to cover tests written using ES6 features? What am I missing?

Answer 1

July 2016

Here are the relevant portions of a package.json file with a working "npm cover" command that is proving useful with es6 module code (i.e. including es6 import and export), babel 6, istanbul-1.0-alpha.2

I am posting this because I had to spend a few hours to happen on a solution from someone else's github issue thread (which now I can not find). There seem to be a lot of "solutions" that no longer solve the coverage issue or can not be easily adapted to other stacks of devDependencies. YMMV.

package.json scripts

 "scripts": {
    "clean": "rm -rf ./build ./doc ; mkdir ./build",
    "build": "node_modules/.bin/babel build src/index.js -o build/index.js",
    "doc": "node_modules/.bin/esdoc -c esdoc.json",
    "lint": "node_modules/.bin/eslint src/index.js",
    "lint-test": "node_modules/.bin/eslint test/index.js",
    "test": "node_modules/.bin/mocha --compilers js:babel-core/register --reporter spec --slow 50 --timeout 60000",
    "cover": "node_modules/.bin/istanbul cover node_modules/.bin/_mocha -- -u exports --compilers js:babel-register --timeout 60000",
    "go": "npm run clean && npm run lint && npm run lint-test && npm run test && npm run build"
  },

package.json devDependencies

 "devDependencies": {
    "babel": "^6.5.2",
    "babel-cli": "^6.10.1",
    "babel-core": "^6.10.4",
    "babel-preset-es2015": "^6.9.0",
    "coveralls": "^2.11.9",
    "esdoc": "^0.4.7",
    "eslint": "^3.0.1",
    "istanbul": "^1.0.0-alpha.2",
    "mocha": "^2.5.3",
    "should": "^8.3.1"
  },

.babelrc

{
  "presets": ["es2015"]
}

.travis.yml

language: node_js

node_js:
  - 6

install:
  - npm install

script:
  - npm run lint
  - npm run lint-test
  - npm run cover

after_script: 
  - "cat coverage/lcov.info | node_modules/coveralls/bin/coveralls.js"

Answer 2

Just got this olved by a helpful guy on the LinkedIn Node.JS group. The command line should be:

node --harmony ./node_modules/istanbul-harmony/lib/cli.js cover --hook-run-in-context ./node_modules/mocha/bin/_mocha -- --R spec --U exports tests

While this is quite cumbersome, you can just drop it in your package.json scripts section, and run npm run cover from command line.