feat: Fail on launcher-, reporter-, or preprocessor-load errors.

Fail out of karma if a launcher, reporter, or preprocessor fails to
load, after attempting to load each of them, and reporting errors for
each load error.

Closes karma-runner#855

lib/launcher.js

@@ -61,13 +61,14 @@ var Launcher = function (emitter, injector) {
         var browser = injector.createChild([locals], ['launcher:' + name]).get('launcher:' + name)
       } catch (e) {
         if (e.message.indexOf('No provider for "launcher:' + name + '"') !== -1) {
-          log.warn('Can not load "%s", it is not registered!\n  ' +
-            'Perhaps you are missing some plugin?', name)
+          log.error('Cannot load browser "%s": it is not registered! ' +
+                    'Perhaps you are missing some plugin?', name)
         } else {
-          log.warn('Can not load "%s"!\n  ' + e.stack, name)
+          log.error('Cannot load browser "%s"!\n  ' + e.stack, name)
         }
 
-        return
+        emitter.emit('load_error', 'launcher', name);
+        return;
       }
 
       // TODO(vojta): remove in v1.0 (BC for old launchers)

lib/server.js

@@ -51,6 +51,8 @@ var Server = function (cliOptions, done) {
 
   this.log = logger.create()
 
+  this.loadErrors = []
+
   var config = cfg.parseConfig(cliOptions.configFile, cliOptions)
 
   var modules = [{
@@ -135,6 +137,10 @@ Server.prototype._start = function (config, launcher, preprocess, fileList, webS
 
   self._fileList = fileList
 
+  this.on('load_error', function(type, name) {
+    self.loadErrors.push([type, name])
+  })
+
   config.frameworks.forEach(function (framework) {
     self._injector.get('framework:' + framework)
   })
@@ -175,6 +181,11 @@ Server.prototype._start = function (config, launcher, preprocess, fileList, webS
           singleRunDoneBrowsers[browserLauncher.id] = false
         })
       }
+
+      if (self.loadErrors.length > 0) {
+        // At least one plugin failed to load.
+        process.exit(1)
+      }
     })
   }