如何在不实际写入数据库的情况下基于Bookshelf / Knex测试模型？

Question

如果我定义我的模型实体而没有像这样指定每个表列：

let bookshelf = require('../config/database');

require('./role');

var User = bookshelf.Model.extend({
    tableName: 'users',
    role: function() {
        return this.hasOne(Role);
    }
});

module.exports = bookshelf.model('user', User);

如何在不写入数据库的情况下创建我的Mocha / Sinon测试？

我尝试过这样一个简单且明显失败的测试：

var sinon = require('sinon');

var user = require('../../models/user');

var sandbox = sinon.sandbox.create();

describe('User model', function () {

    beforeEach(function () {
        sandbox.stub(user);
    });

    afterEach(function () {
        // completely restore all fakes created through the sandbox
        sandbox.restore();
    });

    it('should return empty set before adding anything', () => {
        sinon.assert.callCount(user, 1);
    });

});

然而，实际上我收到了一条错误消息：

  User model
    1) "before each" hook for "should return empty set before adding"


  0 passing (41ms)
  1 failing

  1) User model "before each" hook for "should return empty set before adding":
     TypeError: Attempted to wrap undefined property undefined as function
      at wrapMethod (node_modules/sinon/lib/sinon/util/core/wrap-method.js:70:21)
      at stub (node_modules/sinon/lib/sinon/stub.js:56:44)
      at Object.stub (node_modules/sinon/lib/sinon/collection.js:87:33)
      at Context.<anonymous> (test/models/User.spec.js:10:17)

更新

var ModelsUser = require('../../models/user'),
    User = ModelsUser.User,
    Role = require('../../models/role'),
    chai = require('chai'),
    expect = chai.expect,
    should = chai.should();


var assert = require('assert');

describe('User model', function () {

    var test_usr = {name: 'Test User', username: 'test_usr', role_id: 1};

    beforeEach((done) => {
        // making sure the test user is removed before any test
        User.query().del().then(() => done());
    });

    it('should return empty set before adding anything', (done) => {

        User.forge().count().then(function(total) {
            expect(total).to.equal(0);
            done();
        })
        .catch(err => done(err));
    });

    it('should return a valid user after insert', (done) => {

        User.forge(test_usr)
            .save().then((model) => {
                should.exist(model.id);
                done();
            })
            .catch(err => done(err));

    });

});