eventually helper method for making assertions against asynchronous systems

gistfile1.txt

# usage:
# it "should return a result of 5" do
#   eventually { long_running_thing.result.should eq(5) }
# end
module AsyncHelper
  def eventually(:options = {})
    timeout = options[:timeout] || 2
    interval = options[:interval] || 0.1
    time_limit = Time.now + timeout
    loop do
      begin
        yield
      rescue => error
      end
      return if error.nil?
      raise error if Time.now >= time_limit
      sleep interval
    end
  end
end

# Can we put this into RSpec somewhere?

Wouldn't this peg the CPU and possibly starve the thing you're waiting for?

Good point. Needs to take a nap in the loop. Updated.

@mattwynne Looks like there is a syntax error on line 6 with the colon.

@mitchlloyd https://gist.github.com/justinrolston/6974426/12b41c682f83a75c8c93c0a8242e7b8813e802e7#file-gistfile1-txt resolves line 6

Stumbled across this, and realised that the gist no more works since rspec expectation failure now subclasses from Exception rather than StandardError (rspec/rspec-expectations@eafa55d#diff-f14d34de26325e61579baa36128c97cb)

Here's a fork that rescues both StandardError and RSpec::Expectations::ExpectationNotMetError:
https://gist.github.com/xam7247/290868f3c6f0f72e9b01

with returning the result so that user = eventually { User.last! } works for instance

module Helpers::Eventually
  def eventually(timeout: 2, &block)
    maximum_at = Time.zone.now + timeout

    loop do
      begin
        result = block.call
      rescue => error
        raise error if Time.zone.now >= maximum_at
      else
        return result
      end
    end
  end
end