w00t

calc.js

var ops = {
	"-": function (num1, num2) { return num1 - num2; },
	"*": function (num1, num2) { return num1 * num2; },
	"+": function (num1, num2) { return num1 + num2; }
};

module.exports = function (str) {

	var args = str.split(" ");

	var num1 = parseInt(args[0], 10),
		action = args[1],
		num2 = parseInt(args[2], 10);

	return ops[action](num1, num2);

};

calc.test.js

var buster = require('buster');
var expect = buster.referee.expect;
var calculate = require('../src/calc');

buster.testCase("calc", {

	"should sum 2 numbers": function () {
		expect(calculate("1 + 1")).toEqual(2);
	},

	"should subtract 2 numbers": function () {
		expect(calculate("2 - 1")).toEqual(1);
	},

	"should multiply 2 numbers": function () {
		expect(calculate("2 * 3")).toEqual(6);
	},

	"should use actual numbers for multiplication": function () {
		expect(calculate("2 * 4")).toEqual(8);
	},

	"should use actual numbers for addition": function () {
		expect(calculate("2 + 4")).toEqual(6);
	}

});