This moment is a phase of the iterative process of developing an idea that enables get feedback from your target audience. The purpose of the test is learning what works and what does not while taking calculated risks.
The testing phase has to be prepared base on the stage of the idea development (early or advanced). At initial stages, we will opt for qualitative models, while, in mature phases, we will seek to reach as many users as possible. On the test, our goal is not just catching the user opinion but understand the rational party (what he says and does regarding our solution), as well as the emotional party (what we observe and understand that he opines and feels regarding our solution).