Rspec exception getting caught by async method

gistfile1.rb

require 'celluloid'

# It wasn't until I commented out this line that I realised what was actually going on below
# Celluloid.logger = nil

class Foo
  include Celluloid
  def do
    bar
  end
  def bar; end
end

describe Foo do
  let(:instance){Foo.new}
  it 'should detect a message being sent' do
    expect(instance.wrapped_object).to receive(:bar)
    instance.async.do
    sleep 0.1
  end
  it 'THIS TEST SHOULD FAIL' do
    expect(instance.wrapped_object).to_not receive(:bar)
    instance.async.do
    sleep 0.1
  end
end

Sorry, I never got a notification about your response. But thanks. I seem to remember I fixed it by taking a completely different approach. I do still sometimes find myself using sleeps in Celluloid specs, which can't be good. I just need to be more imaginative I think.