Prime number calculator
Aiming at your questions, your naming conventions are good. However, in your test you tend to switch between camelCase and words_separated_by_underscores. I would suggest sticking to one or the other (we tend to use underscores). Your algorithm looks good and taking ANeves suggestions will make it look more "Ruby"ish.

However, I am going to suggest a much more efficient way of generating your prime numbers and none prime numbers in your Test. Instead of typing each prime number between 1 and 100 by hand into an Array, you could use the Array#Select method. It takes in an Enumerator, runs a given block against each item passed in, and returns an Array of only the items that return true. 

prime_numbers = (1..100).select {|num| num.prime?}


This will given you the same Array you got by typing it all in manually. You can do the same for the none prime numbers.

non_prime_numbers = (1..100).select {|num| num unless num.prime?}


This'll return num only if it is not prime.

It'll save you a lot of typing and it will look more "Ruby"ish.