Is there a mold test kit for packaged food?
A household mold test is going to test for the sort of mold which causes problems for buildings. It's a very different organism than that found in food.
The main thing you need to consider is whether you know what mold tastes like. Spoiled food will taste strange in many different ways, so if you're associating what you're tasting with a moldy food you had, you might be recognizing something completely different.
It strikes me that vitamin gums and chocolate chips are both at least somewhat likely to be coated with a small amount of cornstarch to prevent sticking. You should look at the ingredient labels and see if that, or some other ingredient, is common to them. I've heard of people who dislike the taste of cornstarch.