[ractor] Implement feedback when testing ractors

Author: josacar

Diff for: language/fixtures/shareable_constant_value_magic_comment.rb

@@ -1,9 +1,9 @@
 # shareable_constant_value: literal
 
-A = [1, 2]
-H = {a: "a"}
+A = "rac"
+H = "tor"
 
 Ractor.new do
-  A
-  H
-en.take
+  print A
+  print H
+end.take

Diff for: language/ractor_spec.rb

@@ -1,33 +1,32 @@
-require_relative '../spec_helper'
+require_relative "../spec_helper"
 
-describe "Magic comments" do
+describe "magic comments in ractors" do
   ruby_version_is "3.0" do
-    it 'makes constants shareable between ractors' do
-      -> { ruby_exe(fixture(__FILE__, 'shareable_constant_value_magic_comment.rb'), options: '-W0')}.should_not raise_error
+    it "makes constants shareable between ractors" do
+      out = ruby_exe(fixture(__FILE__, "shareable_constant_value_magic_comment.rb"), options: "-W0")
+      out.should == "ractor"
     end
 
-    it 'makes constants shareable between ractors' do
-      a, b, c = Class.new.class_eval("#{<<~"begin;"}\n#{<<~'end;'}")
-      begin;
+    it "makes constants shareable between ractors" do
+      a, b, c = Class.new.class_eval(<<~RUBY, __FILE__, __LINE__ + 1)
         # shareable_constant_value: experimental_everything
         A = [[1]]
         # shareable_constant_value: none
         B = [[2]]
         # shareable_constant_value: literal
-        C = [["shareable", "constant#{nil}"]]
+        C = [["shareable", "constant#{self.class.name}"]]
         [A, B, C]
-      end;
+      RUBY
       Ractor.shareable?(a).should == true
       Ractor.shareable?(b).should == false
       Ractor.shareable?(c).should == true
     end
 
-    it 'raises an error whenn shared constant is not a literal' do
-      -> { Class.new.class_eval("#{<<~"begin;"}\n#{<<~'end;'}", /unshareable expression/) }.should raise_error
-      begin;
+    it "raises an error when shared constant is not a literal" do
+      -> { Class.new.class_eval(<<~RUBY, __FILE__, __LINE__ + 1) }.should raise_error(Ractor::IsolationError, "cannot assign unshareable object to C")
         # shareable_constant_value: literal
         C = ["Not " + "shareable"]
-      end;
+      RUBY
     end
   end
 end