using ES2015 with mocha, karma and headless chrome for testing - mocha.js

Question

I have a problem with setting up a test environment for a single page application. I am able to run my tests with headless chrome via karma and mocha but I can´t write tests with ES6 Syntax.
My current start command is
karma start --browsers ChromeHeadless karma.config.js --single-run
my karma.config.js
module.exports = function(config) {
config.set({
frameworks: ['mocha', 'chai'],
files: ['test/**/*spec.js'],
reporters: ['nyan'],
port: 9876, // karma web server port
colors: true,
logLevel: config.LOG_INFO,
browsers: ['ChromeHeadless'],
autoWatch: true,
singleRun: false, // Karma captures browsers, runs the tests and exits
concurrency: Infinity,
})
}
I am able to write normal tests but cant use ES6 Syntax here. When I try to import some react components I get this error:
HeadlessChrome 0.0.0 (Linux 0.0.0)
Uncaught SyntaxError: Unexpected token import
at http://localhost:9876/base/test/components.spec.js?b89d2ba6de494310860a60ad2e9e25aea5eb3657:2
So I have to setup babel somehow to compile my test files first. When I try to use compilers: ['js:babel-core/register'] in my karma config its not gonna work.
I also have seen that compilers seems to be deprecated soon so I also tried require: ['babel-core/register'] but it still won´t compile to use ES6 for my test files.
Any idea how to configurate my karma file to write my tests with ES6 ?
Just in case its important. This is my webpack.config.js
const path = require('path');
const ServiceWorkerWebpackPlugin = require('serviceworker-webpack-plugin');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const HtmlWebpackPluginConfig = new HtmlWebpackPlugin({
template: './src/index.html',
filename: 'index.html',
inject: 'body'
});
module.exports = {
entry: './src/index.js',
output: {
path: path.resolve('dist'),
filename: 'index_bundle.js'
},
module: {
loaders: [
{test: /\.js$/, loader: 'babel-loader', exclude: /node_modules/},
{test: /\.jsx$/, loader: 'babel-loader', exclude: /node_modules/}
]
},
plugins: [
new ServiceWorkerWebpackPlugin({
entry: path.join(__dirname, 'src/sw.js'),
}),
HtmlWebpackPluginConfig
],
devServer: {
hot: false,
inline: false,
historyApiFallback: true
}
};

Answer 1

To make things more clear here is a sample project (it's fully runnable, you can fill out files and play around). Just two things to mention: I used jamsine instead of mocha and real 'Chrome' browser instead of headless. Runnable via npm run test command.
files structure
/
karma.conf.js
package.json
sample.js
sampleTest.js
webpack.test.config.js
karma.conf.js:
// Karma configuration
module.exports = function(config) {
config.set({
// base path that will be used to resolve all patterns (eg. files, exclude)
basePath: '',
// frameworks to use
// available frameworks: https://npmjs.org/browse/keyword/karma-adapter
frameworks: ['jasmine'],
// list of files / patterns to load in the browser
files: ['*Test.js'],
// list of files to exclude
exclude: [],
// preprocess matching files before serving them to the browser
preprocessors: {
'*Test.js': [ 'webpack'] //preprocess with webpack
},
// test results reporter to use
reporters: ['progress'],
// setting up webpack configuration
webpack: require('./webpack.test.config'),
// web server port
port: 9876,
// enable / disable colors in the output (reporters and logs)
colors: true,
// level of logging
// possible values: config.LOG_DISABLE || config.LOG_ERROR || config.LOG_WARN || config.LOG_INFO || config.LOG_DEBUG
logLevel: config.LOG_INFO,
// enable / disable watching file and executing tests whenever any file changes
autoWatch: true,
// start these browsers
browsers: ['Chrome'],
// if true, Karma captures browsers, runs the tests and exits
singleRun: true,
// Concurrency level how many browser should be started simultaneous
concurrency: Infinity
})
}
package.json (only relevant stuff):
{
"scripts": {
"test": "node_modules/karma/bin/karma start karma.conf.js"
},
"devDependencies": {
"babel-core": "^6.26.0",
"babel-loader": "^7.1.2",
"babel-preset-env": "^1.6.1",
"jasmine-core": "^2.8.0",
"karma": "^2.0.0",
"karma-chrome-launcher": "^2.2.0",
"karma-jasmine": "^1.1.1",
"karma-webpack": "^2.0.9",
"webpack": "^3.10.0"
}
}
sample.js:
export default function(data){
return data;
}
sampleTest.js:
import sample from 'sample';
describe('Sample', function(){
it('is defined', function(){
expect(sample).toBeDefined();
});
it('returns argument', function(){
expect(sample(0)).toBe(0);
})
});
webpack.test.config.js:
module.exports = {
module: {
rules: [
{
test: /tests\/.*\.js$/,
exclude: /(node_modules)/,
use: {
loader: 'babel-loader',
options: {
presets: ['babel-preset-env']
}
}
}
]
},
resolve: {
modules: ["node_modules", './'],
extensions: [".js"]
}
};
Karma's webpack plugin is used to inform karma that it should prepare files using webpack and specific webpack configuration before sending them to the browser.
Please note key points:
test files pattern in karma.conf.js
pattern to preprocess files (should match the pattern above)
webpack entry in karma.conf.js file
module entry in webpack.test.config.js
p.s. personally I don't use separate patterns for files, I use a separate file (named, say, tests.webpack.js) to have a single place where the way to find test files is defined:
//make sure you have your directory and regex test set correctly
var context = require.context('.', true, /.*Test\.js$/i);
context.keys().forEach(context);
and have in karma.conf.js (paths are irrelevant to sample project above):
files: [
'tests/tests.webpack.js',
],
preprocessors: {
'./tests/tests.webpack.js': [ 'webpack'] //preprocess with webpack
}

Answer 2

You need to convert ESModule in commonjs module with the babel-plugin-transform-es2015-modules-commonjs plugin
In your .babelrc file :
{
"plugins": [
"transform-es2015-modules-commonjs"
]
}
Update :
You can set the plugin in your webpack configuration :
{
loader: 'babel-loader',
options: {
presets: ['#babel/preset-env'],
plugins: [require('#babel/plugin-transform-es2015-modules-commonjs')]
}
}