TDD callback testing sample

logReader.js

var fs = require('fs');

var logReader = {
  getLogEntries : function(logDate, callback){
    if(!(logDate instanceof Date))
      throw new Error('date must be of type Date');

    var logFileName = logDate.toDateString() + '.log';

    fs.readFile(logFileName, function(err, data){
      if(err)
        callback(err);
      else
        callback(null, data.split('\n'));
    });
  }
};

module.exports = logReader;

logReader_tests.js

var logReader = require('./logReader');
var should = require('should')
  , sinon = require('sinon')
  , fs = require('fs');

describe('logReader', function(){
  describe('getLogEntries(logDate, callback)', function(){
    beforeEach(function(){
      // spy out fs method that reads files
      this.oldReadFile = fs.readFile;
      fs.readFile = sinon.spy();
    });
    afterEach(function(){
      // restore readFile method
      fs.readFile = this.oldReadFile;
    });
    it('should callback with error if date is not a Date', function(){
      var date = 123213;
      (function(){
        logReader.getLogEntries(date)
      }).should.throw('date must be of type Date');
    });
    it('should read log file with name of date converted to date string', function(){
      // SETUP
      var logDate = new Date();

      var logFileName = logDate.toDateString() + '.log';

      // TEST
      logReader.getLogEntries(logDate, function(){});
      // SHOULD
      fs.readFile.calledOnce.should.be.ok;
      fs.readFile.firstCall.args[0].should.eql(logFileName);
      fs.readFile.firstCall.args[1].should.be.a('function');
    });
    it('should callback with error if reading log file causes error', function(done){
      // SETUP
      var logDate = new Date();

      var expectedError = new Error('File does not exist');

      var callback = function(err, data){
        // SHOULD
        err.should.eql(expectedError);
        done();
      };

      logReader.getLogEntries(logDate, callback);
      // get first call from readFile, and second argument is the callback.  invoke it with expected error
      var readFileCallback = fs.readFile.firstCall.args[1];
      // TEST
      readFileCallback(expectedError);
    });
    it('should callback with array of log entries from log file contents split by newline', function(done){
      var expectedFileData = "lorum ipsum\ndolurm pidem flummmox\njamarnics\nsdfasdf",
        expectedOutput = ["lorum ipsum","dolurm pidem flummmox","jamarnics","sdfasdf"];

      // SETUP
      var logDate = new Date();

      var callback = function(err, data){
        // SHOULD
        data.should.eql(expectedOutput);
        done();
      };

      logReader.getLogEntries(logDate, callback);
      // get first call from readFile, and second argument is the callback.  invoke it with file contents
      var readFileCallback = fs.readFile.firstCall.args[1];
      // TEST
      readFileCallback(null, expectedFileData);
    });
  })
});

makefile

test:
	@./node_modules/.bin/mocha -R spec $(shell find logReader_tests.js)

.PHONY: test

package.json

{
  "name" : "callbackTesting",
  "version" : "0.0.1",
  "dependencies" : {
  },
  "devDependencies" : {
    "mocha" : "1.0.3",
    "sinon" : "1.4.2",
    "should" : "0.6.3"
  }
}