Add a spec for calling RDATA on a non data wrapper.

Author: aardvark179

lib/truffle/truffle/cext.rb

@@ -1778,7 +1778,7 @@ def rb_tr_log_warning(message)
   end
 
   def RDATA(object)
-    raise TypeError unless Truffle::CExt.hidden_variable_get(object, :data_holder)
+    rb_check_type(object, T_DATA)
     RData.new(object)
   end
 

spec/ruby/optional/capi/data_spec.rb

@@ -30,6 +30,10 @@
       @s.change_struct(a, 100)
       @s.get_struct(a).should == 100
     end
+
+    it "raises a TypeError if the object does not wrap a struct" do
+      lambda { @s.get_struct(Object.new) }.should raise_error(TypeError)
+    end
   end
 
   describe "DATA_PTR" do