old_contents: 'use strict';
  
  const mongo = require('../lib/db');
  
  const User = require('../models/User');
  const Checkin = require('../models/Checkin');
  
  const users = require('./fixtures/users');
  const checkins = require('./fixtures/checkins');
  
  // mongodb connect
  before(function before(done) {
    this.timeout(10000);
  
    if (mongo.connection._hasOpened) {
      process.nextTick(done);
    } else {
      mongo.connection.once('open', done);
    }
  });
  
  // mongodb clean
  beforeEach(() => mongo.connection.db.dropDatabase());
  
  // mongodb insert
  beforeEach(() => Promise.all([
    User.collection.collection.insert(users),
    Checkin.collection.collection.insert(checkins),
  ]));
  
new_contents: 'use strict';
  
  const mongo = require('../lib/db');
  
  const User = require('../models/User');
  const Checkin = require('../models/Checkin');
  
  const users = require('./fixtures/users');
  const checkins = require('./fixtures/checkins');
  
  // mongodb connect
  before(function before(done) {
    this.timeout(10000);
  
    if (mongo.connection._hasOpened) {
      process.nextTick(done);
    } else {
      mongo.connection.once('open', done);
    }
  });
  
  after(() => {
    mongo.models = {};
    mongo.modelSchemas = {};
  });
  
  // mongodb clean
  beforeEach(() => mongo.connection.db.dropDatabase());
  
  // mongodb insert
  beforeEach(() => Promise.all([
    User.collection.collection.insert(users),
    Checkin.collection.collection.insert(checkins),
  ]));
  
subject: clear mongoose model after testing