This directory contains copies of Acid2 and Acid3, based on the copies hosted at acidtests.org after they had ceased being maintained (per the note on that page).
Note these are not maintained here for the sake of providing any useful guide of interoperability or standards compliance, but rather for browser vendors' convenience. It would be inappropriate, therefore, to use them as part of a certification process.
Acid1 can be found at css/CSS2/css1/c5526c-display-000.xht, as it always formed part of the CSS1 testsuite.
The tests themselves (i.e., those at / of their respective subdomains at acidtests.org) are in files named test.html in their respective directories.