This test supersedes the original Acid test.
According to the Web Standards Project website –
“Acid2 is a brand new test designed to push the limits of HTML, CSS, and PNG support in browsers and authoring tools. By testing against Acid2, flaws in support for common web standards are quickly and easily exposed”
Hopefully to be “quickly and easily” fixed by the developers!
There’s a detailed technical guide in case you are curious as to how the test was developed and what it is testing.