The first thing you'll want to do is develop an actual physical prototype or mock-up of your product. This can be done fairly easily with the right product development company. They will help you design a prototype of your product with as little as a simple drawing or just a descriptive idea that you have in your head.
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They can design a 3D model of your product and create a physical mock-up using rapid prototyping. Even if you have a certain packaging in mind, they can design that for you too.
Next is to test the product and its packaging like it would be used in the actual market. How much the product would be twisted, bent, scratched, dropped, etc. to give you a basic idea of what to expect.
Keep in mind that some prototyping materials might be stronger or weaker than the actual material you use for the final product but will still give you a good idea of where your weak spots are and how the product feels/looks to the end-user. The last thing you would want is to sell a product that doesn't work like it should or can't do what the product has promised to do.
You'll also want to get the opinions of people who could use the product or if it's for general use, you could just ask a couple of random people what they think of the product.