Testosterone is an injection preparation containing testosterone (no ester) in the oil base.
In the bodybuilder, "base" is known to be a very effective mass agent. It is usually listed as the most potent injectable steroid available, leading to an incredible rapid growth in muscle mass and strength.
This is mainly due to the very rapid effect of the drug, since the water-based steroids begin to enter the bloodstream almost immediately after administration of the injection. Unlike longer esters, such as heptanoate or cyclopentamate, it takes several weeks for the blood to reach the maximum level of treatment, based on just a few days. Obviously, the metabolic effect of this testosterone will be much faster than what we expect for oil-based (esterification) preparations.