I think this could better be expressed like so;

``` ruby
def registered_worker_names
  client.workers.counts.map { |w| w['name'] }
end

it 'removes deregistered workers' do
  q.put(Qless::Job, {"test" => "workers_reput"})
  q.pop

  expect {
    client._deregister_worker.call([], [q.worker_name])
  }.to change { registered_worker_names }.from([q.worker_name]).to([])
end
```

What do you think?