Problematic fixture module

fixtures.js

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

// Clean up database
function cleanUp(Model, callback) {
  Model.remove({}, function(err) {
    Model.find({}, function(err, docs) {
      assert.equal(docs.length, 0, 'Documents should not exist, found ' + docs.length);
      callback(err);
    });
  });
}

// Test in a clean database
function inClean(Model, fixtures, perform) {
  var series = [
    function initialCleanup(callback) {
      cleanUp(Model, callback);
    }
  ];

  if (fixtures && fixtures.length) {
    fixtures.forEach(function(fixture) {
      series.push(function addDocument(callback) {
        var document = new Model(fixture);
        document.save(function(err, doc) {
          callback(err);
        });
      });
    });
    series.push(function checkDocuments(callback) {
      Model.find({}, function(err, docs) {
        assert.equal(docs.length, fixtures.length, 
                     'Number of loaded docs incorrect: expected ' + fixtures.length + ' got ' + docs.length);
        callback(err);
      });
    });
  }
  
  series.push(function performTest(callback) {
    perform(callback);
  });
  series.push(function finalCleanup(callback) {
    cleanUp(Model, callback);
  });

  async.series(series);
}

exports.cleanUp = cleanUp;
exports.inClean = inClean;