Reply for https://twitter.com/naichilab/status/689325554210754560

controller_spec.rb

context '有効なパラメータの場合' do
  before do
    @user = attributes_for(:user)
  end
  it '正しく登録されること' do
    expect{
      post :create, user: @user
    }.to change(User, :count).by(1)
    expect(response.status).to eq 302
    expect(response).to redirect_to root_path
  end
end