Add test case for custom error's toString.

test/mjsunit/error-tostring.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 65 matching lines @@
 }
 
 assertEquals(["Error",[1,3]], testErrorToString(undefined, undefined));
 assertEquals(["e1",[1,2,3]], testErrorToString("e1", undefined));
 assertEquals(["e1: null",[1,2,3,4]], testErrorToString("e1", null));
 assertEquals(["e1",[1,2,3,4]], testErrorToString("e1", ""));
 assertEquals(["Error: e2",[1,3,4]], testErrorToString(undefined, "e2"));
 assertEquals(["null: e2",[1,2,3,4]], testErrorToString(null, "e2"));
 assertEquals(["e2",[1,2,3,4]], testErrorToString("", "e2"));
 assertEquals(["e1: e2",[1,2,3,4]], testErrorToString("e1", "e2"));
+
+
+// Test that a custom error object does not use Error.prototype.toString.
+
+function MyError(name, message) {
+  this.name = name;
+  this.message = message;
+}
+
+MyError.prototype = Object.create(Error.prototype);
+MyError.prototype.toString = function() {
+  return 'MyError toString';
+};
+
+try {
+  throw new MyError('name', 'message');
+} catch (e) {
+  assertEquals('MyError toString', e.toString());

[arv (Not doing code reviews), 2012/05/21 16:40:03]

I don't think this tests the right thing. This just calls our toString. What we
need to test is that v8::Message uses our toString.

This test would pass before the code change too.

+}