Clemson and FSU were scheduled to play today at 12:00, but the game was postponed this morning.  Clemson already travelled to Tallahassee.  From the ESPN story:  

ACC protocols state teams must be tested the day before competition, so both Florida State and Clemson got tested Friday per conference rules. Those tests are done by an independent third party, and results are received either the same day or early the following day. Once those tests are received, both schools get on a call with the ACC to sign off on whether they feel comfortable proceeding with the game. This is standard before any ACC game can be played.

In this case, Florida State and Clemson could not agree to move forward with the game. Clemson did make the trip to Tallahassee fully intending on playing the game.

Interesting that the game was called at the last minute and that Clemson had every intention of playing.