test: Use Ractor#value

Author: kou

test/test-ractor.rb

@@ -1,8 +1,12 @@
-class RactorTest < Test::Unit::TestCase
-  def setup
-    omit("require Ractor") unless defined? Ractor
+if defined?(Ractor)
+  class Ractor
+    alias_method :value, :take unless method_defined?(:value)
   end
+end
 
+
+class RactorTest < Test::Unit::TestCase
+  ractor
   test("Array#mean") do
     r = Ractor.new do
       [1, 2, 3, 4].mean