Revert "remove debug code."

This reverts commit 65768c80be.

test/ruby/test_rand.rb

@@ -2,6 +2,9 @@
 require 'test/unit'
 
 class TestRand < Test::Unit::TestCase
+  def teardown
+    raise if srand == 0
+  end
   def assert_random_int(ws, m, init = 0)
     # call srand in another process
     assert_separately [], %Q{