title: Getting grunt karma to run one unit test
body: <p>I was wondering if anyone has got grunt karma to run just one spec that is changed on watch. This is my config below. The problem is that the line grunt.config('karma.unit.options.files', filepath); doesn't seem to be doing anything as all the specs still get run however foo does get output before the karma:unit:run gets fired.</p>
  
  <pre><code>grunt.initConfig({
      karma: {
          unit: {
              configFile: 'karma.conf.js',
              background: true,
              singleRun: false,
              options: {
                  files: allFilesArray
              }
          }
      },
      watch: {
          options: {
              spawn: false,
              livereload: true
          },
          karma: {
              files: ['js/spec/**/*.spec.js', 'js/src/**/*.js'],
              tasks: ['karma:unit:run']
          }
      }
  })
  
  grunt.event.on('watch', function (action, filepath){
      console.log('foo');
      grunt.config('karma.unit.options.files', filepath);
  });
  </code></pre>
  
  <p>Is there anyone out there who has achieved running one spec in the terminal on file change? We have thousands of tests so it is starting to get slow.</p>
  
  <p>Thanks,
  Alex</p>