Now that we've added proper ES 5.1 support, including things like strict mode, the test262 test suite looks much better in Opera. However, you may notice that one of the tests fails. As it happens, this particular test seems to be invalid, so it is supposed to fail in browsers with a proper implementation.
And this highlights a point I made a couple of months ago when yet another "benchmark" from Microsoft's marketing department was making the rounds on the web:
The test262 test suite still isn't finished, and there may be faulty or invalid test cases in addition to all the test cases that have yet to be written.
It might be tempting to portray the test262 test suite results as the final word on ECMAScript 5.1 compatibility, but that is far from the case. In fact, there may be other faulty tests in there.
I hope all Opera users out there will be careful not to misrepresent the test results!
In my opinion, the main focus when discussing ECMAScript 5.1 and test262 is how great this is for interoperability. With all the major browsers implementing the same standard and aiming to conform to the official test suite, interoperability on the web will be be greatly enhanced.
So don't get me wrong. If you had the impression that test262 is of no use, this is far from the truth. It will be a great tool to aid interoperability as it develops further, and more tests are added and invalid tests are fixed or removed.
It's just that it goes beyond mere marketing. It's going to be an important tool to keep the web open to all.