That article is bfore Agassi confessed- I think drug tests are more supported and a lot more are being conducted after his confession, and that the ATP knew also at that time was due for criticism.
The testing procedures implemented by the governing bodies of professional tennis lack the teeth necessary to serve as a major crackdown against rampant cheating. The testing policies are lax and almost strictly "in-competition" which is a joke. Players who juice do it between tournaments or during alleged, ahem, extended "injury" hiatuses. In recent years the "whereabouts" rule has been enacted to discourage players from surreptitiously juicing during their out-of-competition sabbaticals but most of the top players in the game DO NOT GET TESTED, per the article on page 24 of the June 2010 issue of Tennis Magazine.
Again, read the linked article written in 2002 about the state of PED detection on the pro tour. Tennis with regard to PEDs is probably where baseball was during the early 90s; players were cheating, everyone else was either in denial or didn't care or stood to profit immensely from the long ball era that ensued shortly after steroids became commonplace.
How long does the average "rally" last during a pro tennis match? About 4 seconds, that's all. Today's players are bludgeoning the ball by dint of better equipment, advanced string technology, tailored surfaces, improved strength and conditioning programs, siphoning athletes away from basketball and other sports, a trend that's ratcheted up the level of athleticism on the tour AND the cocktail of PEDs that some of the players are imbibing.
http://www.smh.com.au/articles/2002/07/11/1026185087993.html