我最近升级到了Rails4，除了我的Rspec测试之外，一切都很好。

require 'spec_helper'

describe Invoice do

  before :each do
    @user = FactoryGirl.create(:activated_user)
    person = FactoryGirl.create(:person, :user => @user, :company => nil)
    @project = FactoryGirl.create(:project, :user => @user, :person_ids => [person.id], :invoice_recipient_id => person.id)
  end

  it "has a valid factory" do
    expect(FactoryGirl.build(:invoice, :project => @project, :user => @user)).to be_valid
  end

  it "is invalid without a number" do
    expect(FactoryGirl.build(:invoice, :project => @project, :user => @user, :number => nil)).to have(1).errors_on(:number)
  end

end

当运行这些测试时，我得到这个错误：

Failure/Error: expect(FactoryGirl.build(:invoice, :project => @project, :user => @user, :number => nil)).to have(1).errors_on(:number)
NoMethodError:
undefined method `have' for #<RSpec::ExampleGroups::Invoice_2:0x009ge29360d910>
# ./spec/models/invoice_spec.rb:16:in `block (2 levels) in <top (required)>'

有谁能告诉我，我错过了什么？
have方法实际上在Rspec中是相当标准的，我不明白为什么它不应该工作。
谢谢你的指点。