But I just tried the search terms "tiananmen square massacre" in PetalSearch. It comes up with the Wikipedia page on the subject, just like Google does.

The second result in PetalSearch points to the rationalwiki, whose text begins "The Tiananmen Square Massacre was a ruthless crackdown on a pro-democracy protest ..."; and that is quoted in the search result.

The next results after that are news items about Chinese censorship:

"China censors tank-shaped Viennetta ice cream on anniversary of Tiananmen Square massacre"

"China Censors Top Livestreamer, Fans Question Potential Link To Tiananmen Square Massacre Reference"

and others.

Seems all right to me.

Of course, I'm not able to repeat this test from within China; but how would Google and others fare there?