RSpec Testing Forked Process

I have a webhook simulator I created for my QA team. In order to prevent the webhooks arriving before the synchronous request completes, I forked the code block that sends the webhook to delay sending for 60s.
I was curious if it is possible to test the code in the forked process with RSpec.

# Code block
Process.detach(
  fork do
    sleep(60)
    hook_resp = Faraday.post(url, webhook_body, 'Content-Type' => 'application/json')
    logger.debug("Pushed to webhook listener, HTTP #{hook_resp.status} received")
  end
)

# RSpec test
it 'should sent to receiver' do
  expect(Faraday).to receive(:post)
    .with('http://web.hook', anything, anything).and_return(double(status: 200))        
  subject.call_method(params)
end

Obviously, I am getting a failing test. Is this testable at all? I do not really care about the response from the webhook receiver, just a fire and forget.