title: RSpec any_instance deprecation: how to fix it?
body: <p>In my Rails project I'm using rspec-mocks using any_instance but I want to avoid this deprecation message:</p>
  
  <p><code>Using any_instance from rspec-mocks' old :should syntax without explicitly enabling the syntax is deprecated. Use the new :expect syntax or explicitly enable :should instead.</code></p>
  
  <p>Here is my specs:</p>
  
  <pre><code>describe (".create") do
    it 'should return error when...' do
      User.any_instance.stub(:save).and_return(false)
      post :create, user: {name: "foo", surname: "bar"}, format: :json
      expect(response.status).to eq(422)
    end
  end
  </code></pre>
  
  <p>Here is my controller:</p>
  
  <pre><code>def create
      @user = User.create(user_params)
      if @user.save
        render json: @user, status: :created, location: @user
      else
        render json: @user.errors, status: :unprocessable_entity
      end
  end
  </code></pre>
  
  <p>I'd like to use the <strong>new :expect syntax</strong> but I can't find how to use it properly.</p>
  
  <p>I'm using RSpec <strong>3.0.2</strong>.</p>