In the context of breaking a pleasure producing habit, such as masturbation (with or without pornography), testosterone plays very little part.
There are two factors at play here:
- Habitualisation - the tendency for an orgasm to repeat behaviours that it has become accustomed to.
- Addiction/Dopamine Response - it feels good so I'm going to carry on.
The first bullet point is obvious, if you've always done something, it's going to make you feel different if you stop. If generally in society it is perceived as being a bad thing (thus making you feel guilty for partaking, even subconsciously), stopping that habit will make you feel good. Especially once you've gotten over the relapse stage.
The second bullet point is more involved. Orgasms, along with the viewing of sexually stimulating material, release dopamine into the blood. Over time, the dopamine receptors in the brain become desensitised and require more and more dopamine to get the same buzz. This is exactly why drug addicts need bigger and bigger doses of their drug. Consequently, once one has stopped partaking in the dopamine producing behaviour the receptors gradually begin to return to normal levels of sensitivity. This results in a generally better mood and a potentially higher libido. To those that don't know the root cause, this increase in mood and libido may appear as though testosterone levels had increased, however, this is likely not the case.