[ruby/timeout] Test that work is done in the same thread/fiber as

the caller
(https://github.com/ruby/timeout/pull/34)

* see discussion in
https://github.com/ruby/timeout/pull/30#issuecomment-1616179651

test/test_timeout.rb

@@ -4,6 +4,15 @@ require 'timeout'
 
 class TestTimeout < Test::Unit::TestCase
 
+  def test_work_is_done_in_same_thread_as_caller
+    assert_equal Thread.current, Timeout.timeout(10){ Thread.current }
+  end
+
+  def test_work_is_done_in_same_fiber_as_caller
+    require 'fiber' # needed for ruby 3.0 and lower
+    assert_equal Fiber.current, Timeout.timeout(10){ Fiber.current }
+  end
+
   def test_non_timing_out_code_is_successful
     assert_nothing_raised do
       assert_equal :ok, Timeout.timeout(1){ :ok }