Olympic athletes are urine tested for testosterone and epitestosterone. The testosterone limit for athletes is a ratio rather than an absolute figure, a 4:1 ratio of testosterone to epitestosterone is the limit.  The human body naturally produces the two at close to a 1:1 ratio, so supplementing testosterone very close to the allowable 4:1 ratio is almost a given for Olympic athletes. This ratio applies to male athletes, while females have to stay under the low end of the average testosterone range of a male. Read on for further details.
Do All Olympians Use Testosterone?
Let’s start with a quote –
You can infer your own answer from that quote.
Can the Test Be Cheated?
The initial ratio test is a urine test. By staying under the 4:1 ratio, Olympians are indeed supplementing testosterone without being caught. If their ratio is above 4:1 then a more advanced test is done to find out if the testosterone was made in the body or artificially. So if a person had extremely high natural testosterone, they should have no issue.
Since the limit is a ratio, you might think that supplementing both testosterone and epitestosterone will keep you under the ratio, but natural and artificial epitestosterone can be distinguished, so there is risk involved there too. 
How Much Does Testosterone Boost Performance?
In our previous article on testosterone, we found that injecting 600mg testosterone for 10 weeks causes testosterone blood serum concentration to increase from around 500 ng/dl to 3000+ ng/dl. That would result in a 6:1 ratio, so Olympic athletes would need to limit their test results to below 2000 ng/dl for the average male athlete to stay below the 4:1 ratio limit. The performance enhancement resulting from 3000+ ng/dl of testosterone is a tripling in muscle gains and a doubling in strength gains. So levels below 2000 ng/dl would likely result in at least a doubling of muscle gains, and 50% more strength gains.
Increasing your testosterone ratio from 1:1 towards 4:1 is a very big advantage and as quoted above, anybody breaking records would not be doing so without an unnatural boost.