generate new test that did already exist & update all module snippets with declaration

test/isPrime/isPrime.js

@@ -1,4 +1,4 @@
-module.exports = num => {
+module.exports = isPrime = num => {
 const boundary = Math.floor(Math.sqrt(num));
 for (var i = 2; i <= boundary; i++) if (num % i == 0) return false;
 return num >= 2;