There is a list of nouns that are both countable and uncountable. "Chocolate" is from that list.
Example 1: "Martin doesn't eat chocolate." Here it's uncountable, it's not about individual sweets made of chocolate, it's chocolate in general.
Example 2: "Ana had left only 3 chocolates inside the box." Here it's countable, it's about specific pieces of chocolate.
When it comes to "newspaper", I think it's countable. Example: "Karen usually buys 3 newspapers for the week.".
I hope it helps!