Expected behaviour

If a port is changed in the passed configuration before server start (e.g. if EADDRINUSE is thrown for a specified port, the next available is used), it should be respected by server middleware.

Actual behaviour

Middleware use a port that was initially passed in the configuration.

Environment Details

• Karma version (output of karma --version): reproduced in 1.7.1, but should be also actual for 2.0.2
• Relevant part of your karma.config.js file: proxy middleware can be used as an example

proxies: {
  '/img/': '/base/test/images/'
},
port: <specify already used port>

Steps to reproduce the behaviour

1. Run karma instance (karma start) with already used port – in other words you have to raise EADDRINUSE error in

   karma/lib/server.js

   Line 186 in 667b47e

   if (e.code === 'EADDRINUSE') {

   It can be reproduced by running 2 or more karma instances that use the same port (e.g. 9876)
2. You have to see Karma warning: WARN [karma]: Port 9876 in use
   and a new port that Karma uses: INFO [karma]: Karma <v> server started at http://0.0.0.0:9877/

3. Try to load any resources that match proxy rules.
4. Resources are proxied to the initial port 9876 instead of changed 9877.