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title
Testing a Node.js HTTP server with Mocha

I spent the better part of the past week updating a Node.js HTTP server from version 0.4.8 of Node to the most recent version, 0.8.20. I started looking over the change logs but they quickly overwhelmed me. Two years of development on Node, V8, npm, and dependent packages generated a lot of changes.

Instead of trying to reason about what might break, I decided to write tests. That way any breaking changes would break the build. Plus writing tests would allow me to refactor the code in the future and be confident that I didn't break anything.

Server

The server isn't too complicated. It returns an HTTP 200 OK response to every request. It also includes the text "Hello, world!" in the response.

var http = require('http');

this.server = http.createServer(function (req, res) {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello, world!\n');
});

exports.listen = function () {
  this.server.listen.apply(this.server, arguments);
};

exports.close = function (callback) {
  this.server.close(callback);
};

You may notice that the server doesn't start automatically. You have to call listen for anything to happen. Setting up the server like this makes require idempotent, which is a good thing.

Tests

I happen to use Mocha for testing, but the concepts described here should be applicable to other JavaScript test frameworks.

Before getting to the actual tests, there's a little bit of boilerplate to get out of the way. The test suite should fire up the server when it starts and kill the server when it finishes.

var server = require('../lib/server');

describe('server', function () {
  before(function () {
    server.listen(8000);
  });

  after(function () {
    server.close();
  });
});

With that out of the way, it's on to the actual tests. Since the server does so little, it stands to reason that there won't be much to the tests. All they do is check the status code and response body. Exactly what you'd expect.

var assert = require('assert'),
    http = require('http');

describe('/', function () {
  it('should return 200', function (done) {
    http.get('http://localhost:8000', function (res) {
      assert.equal(200, res.statusCode);
      done();
    });
  });

  it('should say "Hello, world!"', function (done) {
    http.get('http://localhost:8000', function (res) {
      var data = '';

      res.on('data', function (chunk) {
        data += chunk;
      });

      res.on('end', function () {
        assert.equal('Hello, world!\n', data);
        done();
      });
    });
  });
});

That's all there is to it! Running the test suite is a piece of cake with npm test.