Add distribution test

test/distribution.js

@@ -0,0 +1,28 @@
+var shortid = require('..')
+
+var COUNT = 100 * 1000
+var LENGTH = shortid().length
+
+var chars = { }
+for (var i = 0; i < COUNT; i++) {
+  var id = shortid()
+  for (var j = 0; j < id.length; j++) {
+    var char = id[j]
+    if (!chars[char]) chars[char] = 0
+    chars[char] += 1
+  }
+}
+
+var ALPHABET = Object.keys(chars).length
+
+var d = Object
+  .keys(chars)
+  .map(i => [i, chars[i]])
+  .sort((a, b) => b[1] - a[1])
+  .map(i => {
+    var probability = i[1] * ALPHABET / (COUNT * LENGTH)
+    console.log(i[0] + '  ' + probability)
+    return probability
+  })
+
+console.log('\nMax. difference: ' + (d[0] - d[d.length - 1]))