Question

I’ve written a feature for my library Rubikon that displays a throbber (a spinning — as you may have seen in other console apps) as long as some other code is running.

To test this feature I capture the output of the throbber in a StringIO and compare it with the expected value. As the throbber is only displayed as long as the other code is running the content of the IO gets longer when the code runs longer. In my tests I do a simple sleep 1 and should have a constant 1 second delay. This works most of the time, but sometimes (apparently due to external factors like heavy load on the CPU) it fails, because the code doesn’t run for 1 second, but for a bit more, so that the throbber prints a few additional characters.

My question is: Is there any possibility to test such time critical features in Ruby?

Answer 1

From your github repository, I found this test for the Throbber class:

should 'work correctly' do
  ostream = StringIO.new
  thread = Thread.new { sleep 1 }
  throbber = Throbber.new(ostream, thread)
  thread.join
  throbber.join
  assert_equal " \b-\b\\\b|\b/\b", ostream.string
end

I’ll assume that a throbber iterates over ['-', '\', '|', '/'], backspacing before each write, once per second. Consider the following test:

should 'work correctly' do
  ostream = StringIO.new
  started_at = Time.now
  ended_at = nil
  thread = Thread.new { sleep 1; ended_at = Time.now }
  throbber = Throbber.new(ostream, thread)
  thread.join
  throbber.join
  duration = ended_at - started_at
  iterated_chars = " -\\|/"
  expected = ""
  if duration >= 1
    # After n seconds we should have n copies of " -\\|/", excluding \b for now
    expected << iterated_chars * duration.to_i
  end
  # Next append the characters we'd get from working for fractions of a second:
  remainder = duration - duration.to_i
  expected << iterated_chars[0..((iterated_chars.length*remainder).to_i)] if remainder > 0.0
  expected = expected.split('').join("\b") + "\b"
  assert_equal expected, ostream.string
end

The last assignment of expected is a bit unpleasant, but I made the assumption that the throbber would write character/backspace pairs atomically. If this is not true, you should be able to insert the \b escape sequence into the iterated_chars string and remove the last assignment entirely.