math.js

exports.abs = function(number){
	return number < 0 ? -number : number;
};

exports.pow = function(x, y){
	var value = 1;

	for( var i = 0; i < y; i++ ){
		value *= x;
	}
	return value;
};

exports.asyncAbs = function(number, cb){
	setTimeout(function(){
		cb(null, exports.abs(number));
	}, 100);
};

test.js

var assert = require('assert');
var math = require('../math');

suite('math test', function(){
	test('math.pow test', function(){
		assert.deepEqual(4, math.pow(2,2));
		assert.deepEqual(1, math.pow(1,2));
	});

	test('math.abs test', function(){
		assert.deepEqual(10, math.abs(-10));
		assert.deepEqual(10, math.abs(10));
	});

	test('math.asyncAbs test', function(done){
		math.asyncAbs(-10, function(err, number){
			assert.ifError(err);
			assert.deepEqual(10, number);
			done();
		});
	});
});