Phonetic key generator to es6 and add some tests

lib/key_generators/phonetic.js

@@ -1,33 +1,27 @@
 // Draws inspiration from pwgen and http://tools.arantius.com/password
-var PhoneticKeyGenerator = function() {
-  // No options
+
+const randOf = (collection) => {
+  return () => {
+    return collection[Math.floor(Math.random() * collection.length)];
+  };
 };
 
-// Generate a phonetic key
-PhoneticKeyGenerator.prototype.createKey = function(keyLength) {
-  var text = '';
-  var start = Math.round(Math.random());
-  for (var i = 0; i < keyLength; i++) {
-    text += (i % 2 == start) ? this.randConsonant() : this.randVowel();
+// Helper methods to get an random vowel or consonant
+const randVowel = randOf('aeiou');
+const randConsonant = randOf('bcdfghjklmnpqrstvwxyz');
+
+module.exports = class PhoneticKeyGenerator {
+
+  // Generate a phonetic key of alternating consonant & vowel
+  createKey(keyLength) {
+    let text = '';
+    const start = Math.round(Math.random());
+
+    for (let i = 0; i < keyLength; i++) {
+      text += (i % 2 == start) ? randConsonant() : randVowel();
+    }
+
+    return text;
   }
-  return text;
+
 };
-
-PhoneticKeyGenerator.consonants = 'bcdfghjklmnpqrstvwxyz';
-PhoneticKeyGenerator.vowels = 'aeiou';
-
-// Get an random vowel
-PhoneticKeyGenerator.prototype.randVowel = function() {
-  return PhoneticKeyGenerator.vowels[
-    Math.floor(Math.random() * PhoneticKeyGenerator.vowels.length)
-  ];
-};
-
-// Get an random consonant
-PhoneticKeyGenerator.prototype.randConsonant = function() {
-  return PhoneticKeyGenerator.consonants[
-    Math.floor(Math.random() * PhoneticKeyGenerator.consonants.length)
-  ];
-};
-
-module.exports = PhoneticKeyGenerator;