If you use grunt, you can use the grunt-contrib-watch plugin to watch for file changes and run your tests automagically. Your Gruntfile.js should look something like this.

Gruntfile.js

module.exports = function(grunt) {
 grunt.initConfig({
    jshint: {
      files: [],
    },
    watch: {
      files: ['src/**/*.js'],
      tasks: ['jshint']
    }
  });
  grunt.loadNpmTasks('grunt-contrib-jshint');
  grunt.loadNpmTasks('grunt-contrib-watch');
  grunt.registerTask('default', ['watch']);
}