Jack Simon, an ISCA Hall of Fame Coach, likes 30 x 100-yards on 10-seconds rest. 

Get the total time, then subtract the rest time. Then divide by 30. 

• An alternative to a T30 Test Set.

30 x 50s

Avery Adams posted about a test set, 30 x 50 on 1:30. 

Turn the music up and get after it. I typically say 1-second faster than 200 pace. Heart Rate 32.

• Don't allow switching of strokes unless it is to permit two strokes with a switch at 15. So, that's 2 x(15 x 50)
• Another option for the IMers is to do 3 x (10 x 50) with #1-10 fly, #11-20 back, #21-30 breast.