Tests for Fiber scheduler for Kernel.sleep

The test includes a very primitive Fiber scheduler. This one will
probably be extended in future tests.

test/natalie/fiber/scheduler_sleep_test.rb

@@ -0,0 +1,48 @@
+require_relative '../../spec_helper'
+require_relative 'shared/scheduler'
+
+describe 'Fiber.scheduler with Kernel.sleep' do
+  it 'Can interleave fibers with Kernel.sleep' do
+    scheduler = Scheduler.new
+    Fiber.set_scheduler(scheduler)
+    events = []
+
+    sleeper = Fiber.new do
+      events << 'Going to sleep'
+      sleep(0.01)
+      events << 'Woken up'
+    end
+
+    barista = Fiber.new do
+      events << 'Coffee'
+    end
+
+    sleeper.resume
+    barista.resume
+
+    scheduler.close
+
+    events.should == ['Going to sleep', 'Coffee', 'Woken up']
+  end
+
+  it 'Does not interleave fibers without scheduler' do
+    Fiber.set_scheduler(nil)
+    events = []
+
+    sleeper = Fiber.new do
+      events << 'Going to sleep'
+      sleep(0.01)
+      events << 'Woken up'
+    end
+
+    barista = Fiber.new do
+      events << 'Coffee'
+    end
+
+    sleeper.resume
+    barista.resume
+
+    events.should == ['Going to sleep', 'Woken up', 'Coffee']
+  end
+end
+

test/natalie/fiber/shared/scheduler.rb

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+class Scheduler
+  def initialize
+    @waiting = {}
+  end
+
+  def run
+    until @waiting.empty?
+      fiber, = @waiting.find { |fiber, timeout| fiber.alive? && timeout <= current_time }
+      next if fiber.nil?
+
+      @waiting.delete(fiber)
+      fiber.resume
+    end
+  end
+
+  def close
+    run
+  end
+
+  def kernel_sleep(duration)
+    @waiting[Fiber.current] = current_time + duration
+    Fiber.yield
+  end
+
+  def current_time
+    Process.clock_gettime(Process::CLOCK_MONOTONIC)
+  end
+
+  def io_wait(io, events, duration) end
+  def block(blocker, timeout = nil) end
+  def unblock(blocker, fiber) end
+end