feat(launcher): output stderr for failing launchers

lib/launchers/process.js

@@ -77,6 +77,10 @@ var ProcessLauncher = function (spawn, tempDir, timer, processKillTimeout) {
         errorOutput += err.toString()
       }
     })
+
+    self._process.stderr.on('data', function (errBuff) {
+      errorOutput += errBuff.toString()
+    })
   }
 
   this._onProcessExit = function (code, errorOutput) {

test/e2e/launcher-error.feature

@@ -0,0 +1,20 @@
+Feature: Launcher error
+  In order to use Karma
+  As a person who wants to write great tests
+  I want Karma to output stderr if a browser fails to connect.
+
+  Scenario: Broken Browser
+    Given a configuration with:
+      """
+      files = ['launcher-error/specs.js'];
+      browsers = [__dirname + '/launcher-error/fake-browser.sh'];
+      plugins = [
+        'karma-jasmine',
+        'karma-script-launcher'
+      ];
+      """
+    When I run Karma
+    Then it fails with like:
+      """
+      Missing fake dependency
+      """

test/e2e/support/launcher-error/fake-browser.sh

@@ -0,0 +1,4 @@
+#!/bin/bash
+
+echo "Missing fake dependency" 1>&2
+exit 1

test/e2e/support/launcher-error/specs.js

@@ -0,0 +1,5 @@
+describe('something', function () {
+  it('should never happen anyway', function () {
+    expect(true).toBe(true)
+  })
+})