Ruby on rails 如何使用RSpec更新测试模型中的属性

我被RSpec的一个规范困住了。如何更新模型的属性使其为零？在更新控制器规范下进行验证更好吗

下面是一个示例代码

describe User do
  describe ".validation" do
    before(:each) do
      @user = User.create!({
        :username => "dexter_morgan"
      })
    end

    ...

    context "given invalid attributes" do
      # how can I make the username nil?
      it "rejects blank username"
    end
  end
end

这应该够了吧

describe User do
  describe ".validation" do
    before(:each) do
      @user = User.create!({
        :username => "dexter_morgan"
      })
    end

    ...

    context "given invalid attributes" do
      it "rejects blank username" do
        @user.username = nil
        @user.should_not be_valid
      end
    end
  end
end