Rails应用程序工作，但功能规范失败

Question

我在用户模型上有自我加入关系：

class User < ActiveRecord::Base
  has_many   :students, class_name:  "User",
                        foreign_key: "teacher_id"
  belongs_to :teacher,  class_name:  "User"
end

我有一名学生控制员：

class StudentsController < ApplicationController

  def index
    @students = current_user.students
  end

end

索引方法的相应视图如下所示：

%ul#students-list
  - @students.each do |student|
    %li= student.full_name

正如您所料，当我导航到/students时，我可以看到学生列表。耶！

然而，我在Capybara中编写的功能规范失败了。

require 'spec_helper'

describe "Navigating to students" do
  let!(:teacher) { create(:teacher_user) }
  let!(:student) { create(:student_user, teacher: teacher) }

  before do
    login_as teacher
    visit '/students'
  end

  it "displays a list of students" do
    expect(page).to have_selector('ul#students-list li')
  end

end

这是我的工厂：

FactoryGirl.define do
  factory :teacher_user, class: "User" do
    email
    password "asterisk"
    first_name "James"
    last_name "Baldwin"
    association :user_type, factory: :user_type_teacher
  end

  factory :student_user, class: "User" do
    email
    password "asterisk"
    first_name "Yuri"
    last_name "Kochiyama"
    association :user_type, factory: :user_type_student
  end
end