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eventually helper method for making assertions against asynchronous systems
# 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?
@aslakhellesoy
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aslakhellesoy commented Sep 20, 2011

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

@mattwynne
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Author

mattwynne commented Sep 20, 2011

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

@mitchlloyd
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mitchlloyd commented Oct 4, 2013

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

@xam7247
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xam7247 commented Aug 10, 2015

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

@dorianmariefr
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dorianmariefr commented Nov 18, 2021

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                                                                      

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