How to test Redis Lock via Rspec?

We have a Lockable concern that allows for locks via Redis

module Lockable
  extend ActiveSupport::Concern

  def redis_lock(key, options = {})
    Redis::Lock.new(
      key,
      expiration: options[:expiration] || 15,
      timeout: options[:timeout] || 0.1
    ).lock { yield if block_given? }
  end
end

We use this in a Controller method to ensure concurrent requests are handled correctly.

def create
redis_lock(<generated_key>, timeout: 15) do
    # perform_operation
  end

  render json: <data>, status: :ok
end

When testing this action, I want to test that the correct generated_key is being sent to Redis to initiate a lock.

I set up an expect for the Redis::Lock but that returns false always presumably because the request to create is sent mid request and not at the end of it.

expect(Redis::Lock).to receive(:create).once

What is the definition of "correct" here? Wouldn't it be easier to just
test the "correctness" of the producer of that key?