Other way around. We had the Trinity test, Hiroshima & Nagasaki, and then we set off the rest. Unless you meant "preparations" for killing more people with our nuclear weapons, in which case you may be correct.
The latter tests arguably weren't performed to improve the killing capabilities of the bombs but rather to understand the physics and physiological impacts of bomb blasts. Given that it's possible (albeit unlikely) we never see a nuclear weapon used in war again I don't see it as being completely obvious.
