Grunt/Watch/Mocha only run on my changed file

Here is a little snippet to reach on of the lazy people dream :D

First we need a grunt watch task.

grunt.initConfig({
    watch: {
      automatic: {
        files: ['src/**/*.js']
      }
});

There is the worker:

MochaTester = {

      mochaOptions: {
        reporter: 'dot'
      },

      Mocha: require('mocha'),
      path: require('path'),
      fs: require('fs'),

      registerToWatchTask: function(target, mochaOptions){
        var tester = Object.create(this);

        tester.target = target;
        tester.mochaOptions = mochaOptions ? 
                                              mochaOptions : 
                                              this.mochaOptions;

        grunt.event.on("watch", tester.listener.bind(tester));
        return tester;
      },

      listener: function(action, filepath, target)
      {
        if (!this.isListenedEvent(action, target)) {
          return;
        }

        var testFile = this.getTestFilePath(filepath);

        if (filepath != testFile) {
          this.clearCache(filepath);
        }

        this.clearCache(testFile);
        this.createMochaWithFile(testFile);

        setTimeout(this.run.bind(this), 500);
      },

      isListenedEvent: function(action, target)
      {
        return action == 'changed' && target == this.target;
      },

      // */myFile.js
      // */test/myFileTest.js
      // either my file or his test file changed get the test file
      getTestFilePath: function(filepath)
      {
        var isTestFile = filepath.indexOf('Test.js') != -1,
              testFile = !isTestFile ? 
                             filepath.replace(/(.+)\/(\w+)\.js/, '/test/Test.js') : 
                             filepath;

        if (!isTestFile && !this.path.existsSync(filepath)) {
          throw new Error('\nTestFile not found:\n'+filepath)
        }

        return testFile;
      },

      // require cache all time, so second time zero test will execute
      // if does not clear from the cache
      clearCache: function(filepath)
      {
        require.cache[require.resolve('./'+filepath)] = undefined;
      },

      createMochaWithFile: function(filepath)
      {
        this.mocha = new this.Mocha(this.mochaOptions);
        this.mocha.addFile(filepath);
      },

      run: function()
      {
        this.mocha.run(function(failureCount){
          if (failureCount) {
            grunt.log.error('falling: ' + failureCount)
          } else {
            grunt.log.ok('OK');
          }
        });
      }
    }

And something familiar: need to register the task:)

MochaTester.registerToWatchTask('automatic');