An example of how to run node commands from grunt and get the output result

grunt_tests.js

'use strict';

module.exports = function(grunt) {
  grunt.registerTask('runTests', '', function() {
    var done = this.async();

    grunt.util.spawn({
      cmd: 'node',
      args: ['./js/tests/runner/tests.js']
    }, function(e, result) {
      printResult(e, result);
      done();
    });
  });

  function printResult(e, result) {
    if (e) {
      grunt.log.writeln(e);
    } else if (result) {
      grunt.log.writeln(result);
    }
  }
};