def update
    if check_token?
      @user.update(user_params)
      head :no_content
    end
  end

describe 'PUT /users/:id' do
    let!(:user) { User.create(id: 1, email: 'test@mail.ru', password: 'abc123') }

    context '# check success update' do
      before(:each) do
        patch :update, { user: { id: 1, email: 'newmail@example.com' } }
      end

      it 'returns status code 204' do
        expect(response).to have_http_status(204)
      end

    end
  end #<-- end of PUT /users/:id

Failures:

  1) UsersController PUT /users/:id # check success update returns status code 204
     Failure/Error: patch :update, { user: { id: 1, email: 'newmail@example.com' } }

     ArgumentError:
       unknown keyword: user
     # ./spec/controllers/users_controller_spec.rb:37:in `block (4 levels) in <top (required)>'