例子

 describe 'PUT #join_group' do
    before(:each) do
      # allow(controller).to receive_message(:current_user).and_return(user)
      expect_any_instance_of(User).to receive(:join_group)
    end
    let(:course) { create :issue_course, creator: user, group_no: 'group_no', group_id: 'group_id'}
    subject! { put :join_group, id: course}
    it { expect(response).to redirect_to(yt_group_path(course.group_id))}
  end