Autowatch not working with karma-webpack on karma version 4.0

[Mighty683]

• Operating System: Linux Mint
• Node Version: 10.15.1
• NPM Version: 6.4.1
• webpack Version: 3.6.0
• karma-webpack Version: 3.0.5

Expected Behavior

Webpack rebuild bundle on file change when karma-webpack is used with Karma 4.0

Actual Behavior

Nothing happens, Karma notice file change, but test bundle don't change

Code

 // Part of my karma.conf.js

module.exports = function (config) {
  config.set({
    frameworks: ['mocha'],
    files: [{
      pattern: 'test/**/*.spec.js'
    }],

    preprocessors: {
      'test/**/*.spec.js': ['webpack', 'sourcemap']
    },

    webpack: {
      // ...
      module: {
        loaders: [
          {
            test: /\.js$/,
            loader: 'babel-loader',
            exclude: path.join(__dirname, 'node_modules')
          },
          {
            test: /\.vue$/,
            loader: 'vue-loader'
          }
        ]
      }
    },
    // ...
  }) 
}

How Do We Reproduce?

My karma config watches on files placed inside test folder. When I save change in folder, webpack doesn't get changes and test run on old files

#3226 - Seems to be connected with this issue.

Fix

Downgrade Karma to 3.1.4 version fixed the problem.

[perry-mitchell]

Still seeing this on v6.. autoWatch has no effect. Karma simply exits after running tests.