Noah already had an idea on how to proceed for the creation of his new cultivation technique. He had memorized how his body had transformed the primary energy in "Breath" of the darkness element during the transformation. So, the general structure of the "Breath" had been in his mind for a while by then.
However, he had to modify that structure since the resulting energy was weaker than the "Breath" in the environment and didn't express his individuality, which was the main requirement at his level.
His meditations after the transformation though had focused on that issue, so he could claim that he wasn't approaching the testing phase blindly.
The essential feature of a cultivation technique was its ability to gather energy from the environment. Noah had already managed to create that with the Black Hole technique, but he felt that merely improving his old ring wouldn't be enough to express the entirety of his individuality.