The parse-error message asserted by two of the tests has changed since
duktape-2.3.0, it is now

# encoding: ASCII-8BIT
parse error (line 1, end of input)

This should hopefully cover both cases.

--- a/test/test_duktape.rb
+++ b/test/test_duktape.rb
@@ -102,7 +102,7 @@
         @ctx.eval_string('{')
       end
 
-      assert_equal "parse error (line 1)", err.message
+      assert_match /parse error [(]line 1/, err.message
     end
 
     def test_type_error
@@ -160,7 +160,7 @@
         @ctx.exec_string('{')
       end
 
-      assert_equal "parse error (line 1)", err.message
+      assert_match /parse error [(]line 1/, err.message
     end
 
     def test_type_error