Need support for draining queues

[anazar]

It would be great if we could support draining queues similar to how sidekiq does it here: https://github.com/mperham/sidekiq/wiki/Testing#testing-worker-queueing-fake

I would recommend 2 methods:

1. Executing all queued jobs by draining the queue for a specific worker
   HardWorker.drain

2. Draining the entire queue
   Que.drain_all

[ZimbiX]

Some more context in Discord

[bblimke]

@ZimbiX do you have any workaround applied?

[ZimbiX]

@bblimke As mentioned in the linked Discord conversation, you can start a Locker manually, and poll the jobs table row count to wait for completion (if it's for tests, you could use rspec-wait). Something like:

let(:locker) { Que::Locker.new }

let!(:que_sync_orig) { Que.run_synchronously }

before { Que.run_synchronously = false }

after do
  locker.stop!
  db[:que_jobs].delete
  Que.run_synchronously = que_sync_orig
end

it 'drains' do
  TestJob.enqueue
  locker
  with_wait(delay: 0.001) do
    wait_for { db[:que_jobs].count }.to eq(0)
  end
end