karma Uncaught SyntaxError: Unexpected token export - node.js

Question

I use karma + jasmine to write test cases for vue and webpack, and it once worked. But after I upgrade vue for 1 to 2, and update vue-loader accordingly, it starts to give error.
Now when I run karma start karma.config.js, it give me error like:
Chrome 53.0.2785 (Windows 7 0.0.0) ERROR
Uncaught SyntaxError: Unexpected token export
at test/index.js:8995
My karma.config.js is:
var webpackConf = require('./webpack.config.js')
delete webpackConf.entry
module.exports = function (config) {
config.set({
browsers: ['Chrome'],
frameworks: ['jasmine'],
reporters: ['progress', 'html'],
htmlReporter: {
outputFile: 'tests/unit-test.html',
// Optional
pageTitle: 'Unit Tests',
subPageTitle: 'A sample project description',
groupSuites: true,
useCompactStyle: true,
useLegacyStyle: true
},
// this is the entry file for all our tests.
files: [
{pattern: './test/index.js', watched: false},
],
// we will pass the entry file to webpack for bundling.
preprocessors: {
'./test/index.js': ['webpack']
},
// use the webpack config
webpack: webpackConf,
// avoid walls of useless text
webpackMiddleware: {
noInfo: true
},
singleRun: true,
plugins: [
'karma-chrome-launcher',
'karma-jasmine',
'karma-webpack',
'karma-htmlfile-reporter'
]
})
}
My webpack.config.js is:
var path = require('path');
var HtmlWebpackPlugin = require('html-webpack-plugin');
var webpack = require('webpack');
module.exports = {
entry: ['webpack-hot-middleware/client','./index.js'],
output: {
path: path.resolve(__dirname, '../output/static'),
publicPath: '/',
//filename: '[name].[hash].js'
filename: 'main.js'
//chunkFilename: '[id].[chunkhash].js'
},
resolve: {
alias: {
'vue$': 'vue/dist/vue.common.js'
},
extensions: ['', '.js', '.vue']
},
module: {
loaders: [
{
test: /\.vue$/,
loader: 'vue'
},
{
test: /\.js$/,
loader: 'babel?presets=es2015',
exclude: /node_modules/
},
{
test: /\.scss$/,
loaders: ["style", "css", "sass"]
}
]
},
plugins: [
new webpack.optimize.OccurenceOrderPlugin(),
new webpack.HotModuleReplacementPlugin(),
new webpack.NoErrorsPlugin(),
new HtmlWebpackPlugin({
filename: 'index.html',
template: path.resolve(__dirname, 'index.html'),
inject: true
})
]
}
Looks like the es6 export syntax is not translated correctly. Also, I did not know where to take a look at the test/index.js:8995 because this is auto generated by webpack. The real index.js is quite simple, just 2 lines:
var testsContext = require.context('.', true, /\.spec\.js$/)
testsContext.keys().forEach(testsContext)
How to debug this and what can I do to solve the problem?