users_api_spec_v2.rb

let!(:user) { create :user }
before do
  allow(User).to receive(:find).with(user.id).and_return(user)
end

it 'updates the user' do
  expect(user).to receive(:update!).with(name: 'Alex')
  post "/users/#{user.id}", params: { name: 'Alex' }
end