A physical product usually starts as a short list of beliefs. The problem matters. The format is right. The price will hold. The claim will land. Most of those beliefs never get written down, which is what makes them dangerous: an assumption nobody has stated is an assumption nobody can test.
The useful exercise is not to test everything. It is to work out which single belief, if wrong, would change what you do next. For most physical products that is not the one the team is arguing about. Teams argue about the ones they find interesting, and those are usually the ones they have already half-answered.
A rough test: for each belief, ask what you would do differently if it turned out to be false. If the answer is nothing, it does not need evidence. If the answer is that you would not have bought the inventory, that is the one to test first.
The other half of this is being honest about what your existing evidence actually establishes. A concept test tells you people liked an idea described in words. It does not tell you they will like the product. Stated intent is not demand, and the gap between them is where launch budgets go to die.