A huge number of (male) athletes across all sports are doping now. Testosterone deficiency is a medical condition, and taking “testosterone replacement therapy” is explicitly allowed by many sports. Even if it’s not allowed, it’s not really possible to robustly test for, because in some forms at least it’s simply increasing the levels of the same hormones that your body is naturally producing. Same goes for human growth hormone. Just take enough to put your levels at a very high, but plausibly natural level and you essentially can’t fail a drug test.

It’s only called “testosterone replacement therapy” when it’s prescribed by a doctor btw. Taking exactly the same course of medication in any other circumstances is called “taking steroids”.